Like most teachers, I’m not fond of extra credit assignments. The reasons are simple: they’re a lot of extra work (for me) and they can be used to game the system in a way that teaches poor work habits. For these reasons, I have a strict policy of no extra credit*. However, when I create a syllabus for a middle or high school class, I like to include many optional assignments. Doing them does not directly affect grades, but it gives interested students information about the types of resources that are available for them to learn more and it gives struggling students alternate ways to reinforce what they are learning. Another benefit of optional assignments is that they help underscore the idea that there is more to learning than just grades.
Do students ever do the optional assignments? Yes, some do. Of course, many don’t, but the ones who do often report that they find them helpful and interesting.
*There is one exception. On tests I will often give a small number of questions that are easy to answer if students watch a particular science documentary or read a long-form science article that I let them know about in advance. I think of this less as extra credit (because it makes such a small difference to final grades) and more as an incentive to explore interesting, non-textbook sources of scientific knowledge.