Question: It is very tempting to assign extra credit problems that are (a) substantially more difficult than others on the problem set, (b) ask for the history of something we discussed in class, or (c) are related to something just barely outside of the scope of the class.

However, I have never done so because, in my experience, very few professors give extra credit.

* **Why do so few professors assign extra credit (or is this not the case)?**
* **What are the arguments against assigning extra credit problems?**

Answer: 
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> **Why do so few professors assign extra credit?**
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In my experience, the attitude towards extra credit is consistent throughout the department. Nearly every professor in the education department at my university puts extra credit questions on the test, but only a few in the math department do. After chatting with other students and professors, this seems to be common in other universities as well.

According to [this article on Faculty Focus](http://www.facultyfocus.com/seminars/extra-credit-an-undeserved-gift-or-a-second-chance-to-learn/), *of the 362 people who answered the question “Do you give extra credit?” 42 percent said sometimes, 31 percent said often and 27 percent said never.* While this doesn't give a breakdown of what type of extra credit, it's interesting to see that 73% of respondents give extra credit at least some of the time.

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> **What are the arguments against assigning extra credit problems?**
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From [an article on that seminar](http://www.facultyfocus.com/articles/teaching-and-learning/does-extra-credit-have-a-place-in-the-college-classroom/): 

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> According to Weimer, some instructors oppose extra credit because they believe that:
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> * It reinforces students’ beliefs that they don’t have to work hard because whatever they miss they can make up with extra credit.
> * Students who ask for extra credit tend to be those who aren’t working very hard — or those who hope they won’t have to work hard — because some easy extra credit options will be available to them.
> * Time spent on extra credit means less time spent on regular assignments.
> * Extra credit (especially if it’s easy) lowers academic standards.
> * It’s inherently unfair to students who work hard and get it done right the first time.
> * It means more work for already busy teachers.
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**But I disagree with those issues!**

I like giving extra credit problems. I believe extra credit problems that are significantly more difficult and require more analytic thinking on the part of the student are fantastic as long as they're used properly. If you're planning on using extra credit problems, consider what you're trying to achieve by providing those problems. Personally, I want to use extra credit to separate the best students and provide those who have worked extremely hard to understand the concepts some leeway on simple mistakes.

* **Don't weigh them too heavily** - Extra credit should give a good student some extra points to offset "stupid" mistakes but not allow a student to pass without understanding the basics.
* **Do make them difficult** - You're not giving away free points. You want to reward students who understand the concepts you've taught them above and beyond what is required.
* **Do put them at the end and label them properly** - It would be terrible for a student to get stuck on the more difficult extra credit and not have time to finish the main problems in a test.
**Extra credit often leads to problems with curves.** I've heard dialogues like this:

**Student:** *I got 88% overall, I think I deserve an A.*

**Teacher:** *But lots of other students got 90's by answering extra credit.*

Here the grade without extra credit is being compared against a standard of grades with extra credit. So the credit was not "extra" at all, but just a badly-labeled part of the class.

To avoid this, keep two sets of grade books, and don't look at the one with extra credit until you've set grade cutoffs from the one without extra credit.

Or, more easily and more transparently, don't give extra credit at all. Your suggestions a, b, and c sound good for short required written assignments.