diff --git a/src/addons/qbehaviour/deferredcbm/services/handlers/deferredcbm.ts b/src/addons/qbehaviour/deferredcbm/services/handlers/deferredcbm.ts
index f7eabd3ea02..03337eb1447 100644
--- a/src/addons/qbehaviour/deferredcbm/services/handlers/deferredcbm.ts
+++ b/src/addons/qbehaviour/deferredcbm/services/handlers/deferredcbm.ts
@@ -21,6 +21,7 @@ import { CoreQuestionQuestionParsed, CoreQuestionsAnswers, CoreQuestionState } f
 import { CoreQuestionHelper } from '@features/question/services/question-helper';
 import { AddonQbehaviourDeferredCBMComponent } from '../../component/deferredcbm';
 import { CoreQuestionDelegate } from '@features/question/services/question-delegate';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 /**
  * Handler to support deferred CBM question behaviour.
@@ -89,12 +90,12 @@ export class AddonQbehaviourDeferredCBMHandlerService implements CoreQuestionBeh
         answers: CoreQuestionsAnswers,
         component: string,
         componentId: string | number,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // First check if the question answer is complete.
         const complete = CoreQuestionDelegate.isCompleteResponse(question, answers, component, componentId);
         if (complete > 0) {
             // Answer is complete, check the user answered CBM too.
-            return answers['-certainty'] ? 1 : 0;
+            return answers['-certainty'] ? QuestionCompleteGradableResponse.YES : QuestionCompleteGradableResponse.NO;
         }
 
         return complete;
diff --git a/src/addons/qbehaviour/deferredfeedback/services/handlers/deferredfeedback.ts b/src/addons/qbehaviour/deferredfeedback/services/handlers/deferredfeedback.ts
index c0cc4ab2364..477f1804673 100644
--- a/src/addons/qbehaviour/deferredfeedback/services/handlers/deferredfeedback.ts
+++ b/src/addons/qbehaviour/deferredfeedback/services/handlers/deferredfeedback.ts
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 import { Injectable } from '@angular/core';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 import { CoreQuestionBehaviourHandler, CoreQuestionQuestionWithAnswers } from '@features/question/services/behaviour-delegate';
 import { CoreQuestionDBRecord } from '@features/question/services/database/question';
@@ -134,7 +135,7 @@ export class AddonQbehaviourDeferredFeedbackHandlerService implements CoreQuesti
         }
 
         // Answers have changed. Now check if the response is complete and calculate the new state.
-        let complete: number;
+        let complete: QuestionCompleteGradableResponse;
         let newState: string;
 
         if (isCompleteFn) {
@@ -190,7 +191,7 @@ export type isCompleteResponseFunction = (
     answers: CoreQuestionsAnswers,
     component: string,
     componentId: string | number,
-) => number;
+) => QuestionCompleteGradableResponse;
 
 /**
  * Check if two responses are the same.
diff --git a/src/addons/qtype/calculatedmulti/services/handlers/calculatedmulti.ts b/src/addons/qtype/calculatedmulti/services/handlers/calculatedmulti.ts
index 9ef004135dd..f436f232906 100644
--- a/src/addons/qtype/calculatedmulti/services/handlers/calculatedmulti.ts
+++ b/src/addons/qtype/calculatedmulti/services/handlers/calculatedmulti.ts
@@ -18,6 +18,7 @@ import { CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '@features/ques
 import { CoreQuestionHandler } from '@features/question/services/question-delegate';
 import { makeSingleton } from '@singletons';
 import { AddonQtypeMultichoiceHandler } from '@addons/qtype/multichoice/services/handlers/multichoice';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 /**
  * Handler to support calculated multi question type.
@@ -44,7 +45,7 @@ export class AddonQtypeCalculatedMultiHandlerService implements CoreQuestionHand
     isCompleteResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // This question type depends on multichoice.
         return AddonQtypeMultichoiceHandler.isCompleteResponseSingle(answers);
     }
@@ -62,7 +63,7 @@ export class AddonQtypeCalculatedMultiHandlerService implements CoreQuestionHand
     isGradableResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // This question type depends on multichoice.
         return AddonQtypeMultichoiceHandler.isGradableResponseSingle(answers);
     }
diff --git a/src/addons/qtype/ddimageortext/services/handlers/ddimageortext.ts b/src/addons/qtype/ddimageortext/services/handlers/ddimageortext.ts
index 835dfd37fbf..22f2be6416c 100644
--- a/src/addons/qtype/ddimageortext/services/handlers/ddimageortext.ts
+++ b/src/addons/qtype/ddimageortext/services/handlers/ddimageortext.ts
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 import { Injectable, Type } from '@angular/core';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 import { CoreQuestion, CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '@features/question/services/question';
 import { CoreQuestionHandler } from '@features/question/services/question-delegate';
@@ -53,17 +54,17 @@ export class AddonQtypeDdImageOrTextHandlerService implements CoreQuestionHandle
     isCompleteResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // An answer is complete if all drop zones have an answer.
         // We should always receive all the drop zones with their value ('' if not answered).
         for (const name in answers) {
             const value = answers[name];
             if (!value || value === '0') {
-                return 0;
+                return QuestionCompleteGradableResponse.NO;
             }
         }
 
-        return 1;
+        return QuestionCompleteGradableResponse.YES;
     }
 
     /**
@@ -79,15 +80,15 @@ export class AddonQtypeDdImageOrTextHandlerService implements CoreQuestionHandle
     isGradableResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse{
         for (const name in answers) {
             const value = answers[name];
             if (value && value !== '0') {
-                return 1;
+                return QuestionCompleteGradableResponse.YES;
             }
         }
 
-        return 0;
+        return QuestionCompleteGradableResponse.NO;
     }
 
     /**
@@ -108,7 +109,7 @@ export class AddonQtypeDdImageOrTextHandlerService implements CoreQuestionHandle
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
     ): string | undefined {
-        if (this.isCompleteResponse(question, answers)) {
+        if (this.isCompleteResponse(question, answers) === QuestionCompleteGradableResponse.YES) {
             return;
         }
 
diff --git a/src/addons/qtype/ddmarker/services/handlers/ddmarker.ts b/src/addons/qtype/ddmarker/services/handlers/ddmarker.ts
index c8453e83623..38754da8a62 100644
--- a/src/addons/qtype/ddmarker/services/handlers/ddmarker.ts
+++ b/src/addons/qtype/ddmarker/services/handlers/ddmarker.ts
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 import { Injectable, Type } from '@angular/core';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 import { CoreQuestion, CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '@features/question/services/question';
 import { CoreQuestionHandler } from '@features/question/services/question-delegate';
@@ -55,15 +56,15 @@ export class AddonQtypeDdMarkerHandlerService implements CoreQuestionHandler {
     isCompleteResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // If 1 dragitem is set we assume the answer is complete (like Moodle does).
         for (const name in answers) {
             if (name !== ':sequencecheck' && answers[name]) {
-                return 1;
+                return QuestionCompleteGradableResponse.YES;
             }
         }
 
-        return 0;
+        return QuestionCompleteGradableResponse.NO;
     }
 
     /**
@@ -79,7 +80,7 @@ export class AddonQtypeDdMarkerHandlerService implements CoreQuestionHandler {
     isGradableResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         return this.isCompleteResponse(question, answers);
     }
 
@@ -119,7 +120,7 @@ export class AddonQtypeDdMarkerHandlerService implements CoreQuestionHandler {
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
     ): string | undefined {
-        if (this.isCompleteResponse(question, answers)) {
+        if (this.isCompleteResponse(question, answers) === QuestionCompleteGradableResponse.YES) {
             return;
         }
 
diff --git a/src/addons/qtype/essay/services/handlers/essay.ts b/src/addons/qtype/essay/services/handlers/essay.ts
index 45e3053e48d..64d62d75837 100644
--- a/src/addons/qtype/essay/services/handlers/essay.ts
+++ b/src/addons/qtype/essay/services/handlers/essay.ts
@@ -28,6 +28,7 @@ import { CoreObject } from '@singletons/object';
 import { CoreWSFile } from '@services/ws';
 import { makeSingleton, Translate } from '@singletons';
 import { CoreFileHelper } from '@services/file-helper';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 /**
  * Handler to support essay question type.
@@ -150,7 +151,8 @@ export class AddonQtypeEssayHandlerService implements CoreQuestionHandler {
             return;
         }
 
-        if (this.isCompleteResponse(question, answers, component, componentId)) {
+        // Continue check in case the response completion cannot be determined.
+        if (this.isCompleteResponse(question, answers, component, componentId) === QuestionCompleteGradableResponse.YES) {
             return;
         }
 
@@ -201,34 +203,38 @@ export class AddonQtypeEssayHandlerService implements CoreQuestionHandler {
         answers: CoreQuestionsAnswers,
         component: string,
         componentId: string | number,
-    ): number {
+    ):  QuestionCompleteGradableResponse {
 
         const hasTextAnswer = !!answers.answer;
         const uploadFilesSupported = question.responsefileareas !== undefined;
         const allowedOptions = this.getAllowedOptions(question);
 
         if (hasTextAnswer && this.checkInputWordCount(question, <string> answers.answer, undefined)) {
-            return 0;
+            return QuestionCompleteGradableResponse.NO;
         }
 
         if (!allowedOptions.attachments) {
-            return hasTextAnswer ? 1 : 0;
+            return hasTextAnswer ? QuestionCompleteGradableResponse.YES : QuestionCompleteGradableResponse.NO;
         }
 
         if (!uploadFilesSupported || !question.parsedSettings) {
             // We can't know if the attachments are required or if the user added any in web.
-            return -1;
+            return QuestionCompleteGradableResponse.UNKNOWN;
         }
 
         const questionComponentId = CoreQuestion.getQuestionComponentId(question, componentId);
         const attachments = CoreFileSession.getFiles(component, questionComponentId);
 
         if (!allowedOptions.text) {
-            return attachments && attachments.length >= Number(question.parsedSettings.attachmentsrequired) ? 1 : 0;
+            return attachments && attachments.length >= Number(question.parsedSettings.attachmentsrequired)
+                ? QuestionCompleteGradableResponse.YES
+                : QuestionCompleteGradableResponse.NO;
         }
 
         return ((hasTextAnswer || question.parsedSettings.responserequired === '0') &&
-                (attachments && attachments.length >= Number(question.parsedSettings.attachmentsrequired))) ? 1 : 0;
+                (attachments && attachments.length >= Number(question.parsedSettings.attachmentsrequired)))
+                    ? QuestionCompleteGradableResponse.YES
+                    : QuestionCompleteGradableResponse.NO;
     }
 
     /**
@@ -246,16 +252,18 @@ export class AddonQtypeEssayHandlerService implements CoreQuestionHandler {
         answers: CoreQuestionsAnswers,
         component: string,
         componentId: string | number,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         if (question.responsefileareas === undefined) {
-            return -1;
+            return QuestionCompleteGradableResponse.UNKNOWN;
         }
 
         const questionComponentId = CoreQuestion.getQuestionComponentId(question, componentId);
         const attachments = CoreFileSession.getFiles(component, questionComponentId);
 
         // Determine if the given response has online text or attachments.
-        return (answers.answer && answers.answer !== '') || (attachments && attachments.length > 0) ? 1 : 0;
+        return (answers.answer && answers.answer !== '') || (attachments && attachments.length > 0)
+            ? QuestionCompleteGradableResponse.YES
+            : QuestionCompleteGradableResponse.NO;
     }
 
     /**
diff --git a/src/addons/qtype/gapselect/services/handlers/gapselect.ts b/src/addons/qtype/gapselect/services/handlers/gapselect.ts
index 3c2e3e53070..bcb06a93f2c 100644
--- a/src/addons/qtype/gapselect/services/handlers/gapselect.ts
+++ b/src/addons/qtype/gapselect/services/handlers/gapselect.ts
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 import { Injectable, Type } from '@angular/core';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 import { CoreQuestion, CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '@features/question/services/question';
 import { CoreQuestionHandler } from '@features/question/services/question-delegate';
@@ -53,16 +54,16 @@ export class AddonQtypeGapSelectHandlerService implements CoreQuestionHandler {
     isCompleteResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // We should always get a value for each select so we can assume we receive all the possible answers.
         for (const name in answers) {
             const value = answers[name];
             if (!value || value === '0') {
-                return 0;
+                return QuestionCompleteGradableResponse.NO;
             }
         }
 
-        return 1;
+        return QuestionCompleteGradableResponse.YES;
     }
 
     /**
@@ -78,16 +79,16 @@ export class AddonQtypeGapSelectHandlerService implements CoreQuestionHandler {
     isGradableResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // We should always get a value for each select so we can assume we receive all the possible answers.
         for (const name in answers) {
             const value = answers[name];
             if (value && value !== '0') {
-                return 1;
+                return QuestionCompleteGradableResponse.YES;
             }
         }
 
-        return 0;
+        return QuestionCompleteGradableResponse.NO;
     }
 
     /**
@@ -108,7 +109,7 @@ export class AddonQtypeGapSelectHandlerService implements CoreQuestionHandler {
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
     ): string | undefined {
-        if (this.isCompleteResponse(question, answers)) {
+        if (this.isCompleteResponse(question, answers) === QuestionCompleteGradableResponse.YES) {
             return;
         }
 
diff --git a/src/addons/qtype/match/services/handlers/match.ts b/src/addons/qtype/match/services/handlers/match.ts
index 7feb1675a7f..88f64304507 100644
--- a/src/addons/qtype/match/services/handlers/match.ts
+++ b/src/addons/qtype/match/services/handlers/match.ts
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 import { Injectable, Type } from '@angular/core';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 import { CoreQuestion, CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '@features/question/services/question';
 import { CoreQuestionHandler } from '@features/question/services/question-delegate';
@@ -53,16 +54,16 @@ export class AddonQtypeMatchHandlerService implements CoreQuestionHandler {
     isCompleteResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // We should always get a value for each select so we can assume we receive all the possible answers.
         for (const name in answers) {
             const value = answers[name];
             if (!value || value === '0') {
-                return 0;
+                return QuestionCompleteGradableResponse.NO;
             }
         }
 
-        return 1;
+        return QuestionCompleteGradableResponse.YES;
     }
 
     /**
@@ -78,16 +79,16 @@ export class AddonQtypeMatchHandlerService implements CoreQuestionHandler {
     isGradableResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // We should always get a value for each select so we can assume we receive all the possible answers.
         for (const name in answers) {
             const value = answers[name];
             if (value && value !== '0') {
-                return 1;
+                return QuestionCompleteGradableResponse.YES;
             }
         }
 
-        return 0;
+        return QuestionCompleteGradableResponse.NO;
     }
 
     /**
@@ -108,7 +109,7 @@ export class AddonQtypeMatchHandlerService implements CoreQuestionHandler {
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
     ): string | undefined {
-        if (this.isCompleteResponse(question, answers)) {
+        if (this.isCompleteResponse(question, answers) === QuestionCompleteGradableResponse.YES) {
             return;
         }
 
diff --git a/src/addons/qtype/multianswer/services/handlers/multianswer.ts b/src/addons/qtype/multianswer/services/handlers/multianswer.ts
index 5755722ff7a..8babbaa67b2 100644
--- a/src/addons/qtype/multianswer/services/handlers/multianswer.ts
+++ b/src/addons/qtype/multianswer/services/handlers/multianswer.ts
@@ -13,6 +13,7 @@
 // limitations under the License.
 
 import { Injectable, Type } from '@angular/core';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 import { CoreQuestion, CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '@features/question/services/question';
 import { CoreQuestionHandler } from '@features/question/services/question-delegate';
@@ -54,7 +55,7 @@ export class AddonQtypeMultiAnswerHandlerService implements CoreQuestionHandler
     isCompleteResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // Get all the inputs in the question to check if they've all been answered.
         const names = CoreQuestion.getBasicAnswers<boolean>(
             CoreQuestionHelper.getAllInputNamesFromHtml(question.html || ''),
@@ -62,11 +63,11 @@ export class AddonQtypeMultiAnswerHandlerService implements CoreQuestionHandler
         for (const name in names) {
             const value = answers[name];
             if (!value) {
-                return 0;
+                return QuestionCompleteGradableResponse.NO;
             }
         }
 
-        return 1;
+        return QuestionCompleteGradableResponse.YES;
     }
 
     /**
@@ -82,16 +83,16 @@ export class AddonQtypeMultiAnswerHandlerService implements CoreQuestionHandler
     isGradableResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         // We should always get a value for each select so we can assume we receive all the possible answers.
         for (const name in answers) {
             const value = answers[name];
             if (value || value === false) {
-                return 1;
+                return QuestionCompleteGradableResponse.YES;
             }
         }
 
-        return 0;
+        return QuestionCompleteGradableResponse.NO;
     }
 
     /**
@@ -130,7 +131,7 @@ export class AddonQtypeMultiAnswerHandlerService implements CoreQuestionHandler
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
     ): string | undefined {
-        if (this.isCompleteResponse(question, answers)) {
+        if (this.isCompleteResponse(question, answers) === QuestionCompleteGradableResponse.YES) {
             return;
         }
 
diff --git a/src/addons/qtype/multichoice/services/handlers/multichoice.ts b/src/addons/qtype/multichoice/services/handlers/multichoice.ts
index 8f8cfda7e64..5c39ac184f4 100644
--- a/src/addons/qtype/multichoice/services/handlers/multichoice.ts
+++ b/src/addons/qtype/multichoice/services/handlers/multichoice.ts
@@ -20,6 +20,7 @@ import { CoreQuestionHandler } from '@features/question/services/question-delega
 import { CoreObject } from '@singletons/object';
 import { makeSingleton, Translate } from '@singletons';
 import { CoreUtils } from '@singletons/utils';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 /**
  * Handler to support multichoice question type.
@@ -45,7 +46,7 @@ export class AddonQtypeMultichoiceHandlerService implements CoreQuestionHandler
     isCompleteResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         let isSingle = true;
         let isMultiComplete = false;
 
@@ -64,7 +65,7 @@ export class AddonQtypeMultichoiceHandlerService implements CoreQuestionHandler
             return this.isCompleteResponseSingle(answers);
         } else {
             // Multi.
-            return isMultiComplete ? 1 : 0;
+            return isMultiComplete ? QuestionCompleteGradableResponse.YES : QuestionCompleteGradableResponse.NO;
         }
     }
 
@@ -74,8 +75,10 @@ export class AddonQtypeMultichoiceHandlerService implements CoreQuestionHandler
      * @param answers The question answers (without prefix).
      * @returns 1 if complete, 0 if not complete, -1 if cannot determine.
      */
-    isCompleteResponseSingle(answers: CoreQuestionsAnswers): number {
-        return (answers.answer && answers.answer !== '') ? 1 : 0;
+    isCompleteResponseSingle(answers: CoreQuestionsAnswers): QuestionCompleteGradableResponse {
+        return (answers.answer && answers.answer !== '')
+            ? QuestionCompleteGradableResponse.YES
+            : QuestionCompleteGradableResponse.NO;
     }
 
     /**
@@ -91,7 +94,7 @@ export class AddonQtypeMultichoiceHandlerService implements CoreQuestionHandler
     isGradableResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         return this.isCompleteResponse(question, answers);
     }
 
@@ -102,7 +105,7 @@ export class AddonQtypeMultichoiceHandlerService implements CoreQuestionHandler
      * @param answers Object with the question answers (without prefix).
      * @returns 1 if gradable, 0 if not gradable, -1 if cannot determine.
      */
-    isGradableResponseSingle(answers: CoreQuestionsAnswers): number {
+    isGradableResponseSingle(answers: CoreQuestionsAnswers): QuestionCompleteGradableResponse {
         return this.isCompleteResponseSingle(answers);
     }
 
@@ -168,7 +171,7 @@ export class AddonQtypeMultichoiceHandlerService implements CoreQuestionHandler
         question: AddonModQuizMultichoiceQuestion,
         answers: CoreQuestionsAnswers,
     ): string | undefined {
-        if (this.isGradableResponse(question, answers)) {
+        if (this.isGradableResponse(question, answers) === QuestionCompleteGradableResponse.YES) {
             return;
         }
 
diff --git a/src/addons/qtype/numerical/services/handlers/numerical.ts b/src/addons/qtype/numerical/services/handlers/numerical.ts
index d54c28a27ab..496d702f9e3 100644
--- a/src/addons/qtype/numerical/services/handlers/numerical.ts
+++ b/src/addons/qtype/numerical/services/handlers/numerical.ts
@@ -18,6 +18,7 @@ import { makeSingleton, Translate } from '@singletons';
 import { convertTextToHTMLElement } from '@/core/utils/create-html-element';
 import { CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '@features/question/services/question';
 import { CoreObject } from '@singletons/object';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 /**
  * Handler to support numerical question type.
@@ -68,43 +69,45 @@ export class AddonQtypeNumericalHandlerService implements CoreQuestionHandler {
     isCompleteResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         if (!this.isGradableResponse(question, answers)) {
-            return 0;
+            return QuestionCompleteGradableResponse.NO;
         }
 
         const { answer, unit } = this.parseAnswer(question, <string> answers.answer);
         if (answer === null) {
-            return 0;
+            return QuestionCompleteGradableResponse.NO;
         }
 
         if (!question.parsedSettings) {
             if (this.hasSeparateUnitField(question)) {
-                return this.isValidValue(<string> answers.unit) ? 1 : 0;
+                return this.isValidValue(<string> answers.unit)
+                    ? QuestionCompleteGradableResponse.YES
+                    : QuestionCompleteGradableResponse.NO;
             }
 
             // We cannot know if the answer should contain units or not.
-            return -1;
+            return QuestionCompleteGradableResponse.UNKNOWN;
         }
 
         if (question.parsedSettings.unitdisplay !== AddonQtypeNumericalHandlerService.UNITINPUT && unit) {
             // There should be no units or be outside of the input, not valid.
-            return 0;
+            return QuestionCompleteGradableResponse.NO;
         }
 
         if (this.hasSeparateUnitField(question) && !this.isValidValue(<string> answers.unit)) {
             // Unit not supplied as a separate field and it's required.
-            return 0;
+            return QuestionCompleteGradableResponse.NO;
         }
 
         if (question.parsedSettings.unitdisplay === AddonQtypeNumericalHandlerService.UNITINPUT &&
                 question.parsedSettings.unitgradingtype === AddonQtypeNumericalHandlerService.UNITGRADED &&
                 !this.isValidValue(unit)) {
             // Unit not supplied inside the input and it's required.
-            return 0;
+            return QuestionCompleteGradableResponse.NO;
         }
 
-        return 1;
+        return QuestionCompleteGradableResponse.YES;
     }
 
     /**
@@ -120,8 +123,10 @@ export class AddonQtypeNumericalHandlerService implements CoreQuestionHandler {
     isGradableResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
-        return this.isValidValue(<string> answers.answer) ? 1 : 0;
+    ): QuestionCompleteGradableResponse {
+        return this.isValidValue(<string> answers.answer)
+            ? QuestionCompleteGradableResponse.YES
+            : QuestionCompleteGradableResponse.NO;
     }
 
     /**
@@ -207,7 +212,7 @@ export class AddonQtypeNumericalHandlerService implements CoreQuestionHandler {
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
     ): string | undefined {
-        if (!this.isGradableResponse(question, answers)) {
+        if (this.isGradableResponse(question, answers) === QuestionCompleteGradableResponse.NO) {
             return Translate.instant('addon.qtype_numerical.pleaseenterananswer');
         }
 
diff --git a/src/addons/qtype/ordering/services/handlers/ordering.ts b/src/addons/qtype/ordering/services/handlers/ordering.ts
index 2ff30b451a5..8d344b5ee93 100644
--- a/src/addons/qtype/ordering/services/handlers/ordering.ts
+++ b/src/addons/qtype/ordering/services/handlers/ordering.ts
@@ -17,6 +17,7 @@ import { CoreQuestionHandler } from '@features/question/services/question-delega
 import { CoreQuestion, CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '@features/question/services/question';
 import { makeSingleton } from '@singletons';
 import { CoreSites } from '@services/sites';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 /**
  * Handler to support ordering question type.
@@ -39,8 +40,8 @@ export class AddonQtypeOrderingHandlerService implements CoreQuestionHandler {
     /**
      * @inheritdoc
      */
-    isCompleteResponse(): number {
-        return 1;
+    isCompleteResponse(): QuestionCompleteGradableResponse {
+        return QuestionCompleteGradableResponse.YES;
     }
 
     /**
@@ -53,8 +54,8 @@ export class AddonQtypeOrderingHandlerService implements CoreQuestionHandler {
     /**
      * @inheritdoc
      */
-    isGradableResponse(): number {
-        return 1;
+    isGradableResponse(): QuestionCompleteGradableResponse {
+        return QuestionCompleteGradableResponse.YES;
     }
 
     /**
diff --git a/src/addons/qtype/shortanswer/services/handlers/shortanswer.ts b/src/addons/qtype/shortanswer/services/handlers/shortanswer.ts
index 3055ff458ca..489af9a8b5a 100644
--- a/src/addons/qtype/shortanswer/services/handlers/shortanswer.ts
+++ b/src/addons/qtype/shortanswer/services/handlers/shortanswer.ts
@@ -18,6 +18,7 @@ import { CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '@features/ques
 import { CoreQuestionHandler } from '@features/question/services/question-delegate';
 import { CoreObject } from '@singletons/object';
 import { makeSingleton, Translate } from '@singletons';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 /**
  * Handler to support short answer question type.
@@ -43,8 +44,8 @@ export class AddonQtypeShortAnswerHandlerService implements CoreQuestionHandler
     isCompleteResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
-        return answers.answer ? 1 : 0;
+    ): QuestionCompleteGradableResponse {
+        return answers.answer ? QuestionCompleteGradableResponse.YES : QuestionCompleteGradableResponse.NO;
     }
 
     /**
@@ -60,7 +61,7 @@ export class AddonQtypeShortAnswerHandlerService implements CoreQuestionHandler
     isGradableResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         return this.isCompleteResponse(question, answers);
     }
 
@@ -82,7 +83,7 @@ export class AddonQtypeShortAnswerHandlerService implements CoreQuestionHandler
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
     ): string | undefined {
-        if (this.isGradableResponse(question, answers)) {
+        if (this.isGradableResponse(question, answers) === QuestionCompleteGradableResponse.YES) {
             return;
         }
 
diff --git a/src/addons/qtype/truefalse/services/handlers/truefalse.ts b/src/addons/qtype/truefalse/services/handlers/truefalse.ts
index 24a05d9de16..ff686c8566d 100644
--- a/src/addons/qtype/truefalse/services/handlers/truefalse.ts
+++ b/src/addons/qtype/truefalse/services/handlers/truefalse.ts
@@ -19,6 +19,7 @@ import { CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '@features/ques
 import { CoreObject } from '@singletons/object';
 import { AddonModQuizMultichoiceQuestion } from '@features/question/classes/base-question-component';
 import { makeSingleton, Translate } from '@singletons';
+import { QuestionCompleteGradableResponse } from '@features/question/constants';
 
 /**
  * Handler to support true/false question type.
@@ -45,8 +46,8 @@ export class AddonQtypeTrueFalseHandlerService implements CoreQuestionHandler {
     isCompleteResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
-        return answers.answer ? 1 : 0;
+    ): QuestionCompleteGradableResponse {
+        return answers.answer ? QuestionCompleteGradableResponse.YES : QuestionCompleteGradableResponse.NO;
     }
 
     /**
@@ -62,7 +63,7 @@ export class AddonQtypeTrueFalseHandlerService implements CoreQuestionHandler {
     isGradableResponse(
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         return this.isCompleteResponse(question, answers);
     }
 
@@ -97,7 +98,7 @@ export class AddonQtypeTrueFalseHandlerService implements CoreQuestionHandler {
         question: CoreQuestionQuestionParsed,
         answers: CoreQuestionsAnswers,
     ): string | undefined {
-        if (this.isGradableResponse(question, answers)) {
+        if (this.isGradableResponse(question, answers) === QuestionCompleteGradableResponse.YES) {
             return;
         }
 
diff --git a/src/core/features/question/classes/base-question-handler.ts b/src/core/features/question/classes/base-question-handler.ts
index 3edcb57231d..9fdf587405f 100644
--- a/src/core/features/question/classes/base-question-handler.ts
+++ b/src/core/features/question/classes/base-question-handler.ts
@@ -16,6 +16,7 @@ import { Type } from '@angular/core';
 
 import { CoreQuestionQuestionParsed, CoreQuestionsAnswers } from '../services/question';
 import { CoreQuestionHandler } from '../services/question-delegate';
+import { QuestionCompleteGradableResponse } from '../constants';
 
 /**
  * Base handler for question types.
@@ -100,8 +101,8 @@ export class CoreQuestionBaseHandler implements CoreQuestionHandler {
         answers: CoreQuestionsAnswers, // eslint-disable-line @typescript-eslint/no-unused-vars
         component: string, // eslint-disable-line @typescript-eslint/no-unused-vars
         componentId: string | number, // eslint-disable-line @typescript-eslint/no-unused-vars
-    ): number {
-        return -1;
+    ): QuestionCompleteGradableResponse {
+        return QuestionCompleteGradableResponse.UNKNOWN;
     }
 
     /**
@@ -119,8 +120,8 @@ export class CoreQuestionBaseHandler implements CoreQuestionHandler {
         answers: CoreQuestionsAnswers, // eslint-disable-line @typescript-eslint/no-unused-vars
         component: string, // eslint-disable-line @typescript-eslint/no-unused-vars
         componentId: string | number, // eslint-disable-line @typescript-eslint/no-unused-vars
-    ): number {
-        return -1;
+    ): QuestionCompleteGradableResponse {
+        return QuestionCompleteGradableResponse.UNKNOWN;
     }
 
     /**
diff --git a/src/core/features/question/constants.ts b/src/core/features/question/constants.ts
index 11743566159..ea16b58484f 100644
--- a/src/core/features/question/constants.ts
+++ b/src/core/features/question/constants.ts
@@ -37,3 +37,12 @@ export const enum QuestionDisplayOptionsValues {
     VISIBLE = 1,
     EDITABLE = 2,
 }
+
+/**
+ * Possible values for the question complete response or gradable response (compatible).
+ */
+export const enum QuestionCompleteGradableResponse {
+    UNKNOWN = -1,
+    NO = 0,
+    YES = 1,
+}
diff --git a/src/core/features/question/services/question-delegate.ts b/src/core/features/question/services/question-delegate.ts
index 7d9b2bece74..e041acc43b4 100644
--- a/src/core/features/question/services/question-delegate.ts
+++ b/src/core/features/question/services/question-delegate.ts
@@ -19,6 +19,7 @@ import { CoreWSFile } from '@services/ws';
 import { makeSingleton } from '@singletons';
 import { CoreQuestionDefaultHandler } from './handlers/default-question';
 import { CoreQuestionQuestionParsed, CoreQuestionsAnswers } from './question';
+import { QuestionCompleteGradableResponse } from '../constants';
 
 /**
  * Interface that all question type handlers must implement.
@@ -91,7 +92,7 @@ export interface CoreQuestionHandler extends CoreDelegateHandler {
         answers: CoreQuestionsAnswers,
         component: string,
         componentId: string | number,
-    ): number;
+    ): QuestionCompleteGradableResponse;
 
     /**
      * Check if a student has provided enough of an answer for the question to be graded automatically,
@@ -108,7 +109,7 @@ export interface CoreQuestionHandler extends CoreDelegateHandler {
         answers: CoreQuestionsAnswers,
         component: string,
         componentId: string | number,
-    ): number;
+    ): QuestionCompleteGradableResponse;
 
     /**
      * Check if two responses are the same.
@@ -296,7 +297,7 @@ export class CoreQuestionDelegateService extends CoreDelegate<CoreQuestionHandle
         answers: CoreQuestionsAnswers,
         component: string,
         componentId: string | number,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         const type = this.getTypeName(question);
 
         const isComplete = this.executeFunctionOnEnabled<number>(
@@ -305,7 +306,7 @@ export class CoreQuestionDelegateService extends CoreDelegate<CoreQuestionHandle
             [question, answers, component, componentId],
         );
 
-        return isComplete ?? -1;
+        return isComplete ?? QuestionCompleteGradableResponse.UNKNOWN;
     }
 
     /**
@@ -323,7 +324,7 @@ export class CoreQuestionDelegateService extends CoreDelegate<CoreQuestionHandle
         answers: CoreQuestionsAnswers,
         component: string,
         componentId: string | number,
-    ): number {
+    ): QuestionCompleteGradableResponse {
         const type = this.getTypeName(question);
 
         const isGradable = this.executeFunctionOnEnabled<number>(
@@ -332,7 +333,7 @@ export class CoreQuestionDelegateService extends CoreDelegate<CoreQuestionHandle
             [question, answers, component, componentId],
         );
 
-        return isGradable ?? -1;
+        return isGradable ?? QuestionCompleteGradableResponse.UNKNOWN;
     }
 
     /**