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?
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, 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.
What are the arguments against assigning extra credit problems?
From an article on that seminar:
According to Weimer, some instructors oppose extra credit because they believe that:
- 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.
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.
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.
I dislike "extra credit" for many reasons, many of which have been mentioned already. But mostly, I think that the argument of Students like bonus problems...I think they [with the reward of extra credit] encourage doing more than was necessary while studying (which I believe to be roughly the standard argument, but this is (essentially) a quote from Tim Seguine in the comments) just isn't good enough. In the real world money is not the only motivation, and I would not like it if, for example, the police force was driven by money rather than a desire to make where I live a safe place. Similarly, if we replace "money" with "final grade" then I do not think it is healthy to motivate students solely by their final grade. I believe an alternative motivation can and should be used in place of "extra credit". For example: Chocolate.
More concretely, I tell my students that if they can find an error in my notes or in my problem sheets then they should come to my office and I will reward them with chocolate (in their answer, vonbrand says that they reward this with extra credit). This means that they can argue all they like about whether or not they deserve chocolate (they point out the errors, but they do it in lectures!), but ultimately the arguments are in good humour as they are arguing over...a piece of chocolate. Additional "extra credit" questions which are meant to motivate the students now become competitions where the winners get, say, a not-quite-the-cheapest box of chocolates. Now, because the rewards are chocolate everything is fun while the students remain motivated (well, enough of them remain motivated to keep me happy), so this all adds to the student experience. I believe that if I replaced "chocolate" with "extra credit" then there would be no improvement in the student's grasping of the subject and I would enjoy lecturing much less.
I give extra credits routinely, mostly to reward not-asked-for work (point out an error in the class notes, suggest an interesting alternative solution for an exam or homework problem, ...) and sometimes for extra homework assigned. In my (by now extensive) experience, students who go the mile to get extra credit would get good or outstanding grades even without the extra points. A very few of those hanging in the balance get over the bump by this, but then they have shown enough insight to merit a passing grade.
In exams I asign a few extra points, but not a problem marked specially. That gives some leeway for mistakes and still getting a perfect score. My exams are typically a fairly simple, general question ("do you even know what we are talking about?") and the remainder several more difficult problems covering the material about evenly. Sometimes questions have a "bonus track" part, if it makes sense to look somewhat further.
