One of the most exciting things in teaching is to hear students begin to ask great question. Great questions come when a student grasps what is being taught and sees a further application of the principle. Or a student understand the concept but sees a situation in which it does not seem to apply. Great questions, contrary to what we think intuitively, demonstrate understanding and knowledge.
I am collecting great questions on this web page to demonstrate to students in the future. Some of their "greatness" depends upon the timing and the context, like a good joke. Nonetheless, they are here for you to enjoy and - maybe - learn from.
For asking a great question, students can use it toward 5% credit on a test (summative or formative) or they even use their questions, if they have the most in their class, to SKIP a test with no penalty (grade is excused in the gradebook.) That demonstrates how much great questions are worth!