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There is not a native feature in Canvas New Quizzes for designating a particular question as "extra credit." However there is a way to do it correctly (and incorrectly). The following describes the most effective method. Note: there is no method that does not require manual grading.
1. When you begin building a New Quiz, you will first be prompted to enter some Quiz settings on what's called the "Assignment Settings" for the Quiz. You must enter total points on this page.
The total point value entered on this page must match the sum of the points for all questions on the quiz. For example, if you have a quiz with 10 questions, worth one point each, plus an extra credit question, the point value in assignment settings should be set to 10.
2. Click "Build" to begin adding questions to the quiz. Add all regular questions to the quiz and set the appropriate point value for each.
3. Add your extra credit question, and set the point value to Zero. You may indicate the "real" point value of the question in the Question Title and/or Question Stem as illustrated below:
4. After the student has submitted their Quiz, the instructor must manually enter the desired number of points for the extra credit question. The Quiz engine can automatically mark the question correct/incorrect, but will not add the points to the student's score (because the Quiz thinks the question is worth zero points).
5. After entering the points for each Extra Credit question, click "Update" at the bottom of the quiz. The "Final Score" will update after clicking this button. Note: You do NOT need to click "Regrade" for each question after entering points. Just enter the points and then click Update when finished.
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There are a variety of other ways to offer extra credit points towards individual assignments or course total grades as a whole. Several of these methods are described in detail (with screen shots) in the following Canvas Guide: How do I give extra credit in a course? Many of these same methods are demonstrated in this 5-minute video from In structure.