Adam,
A bonus question offered to all students is probabbly a good way to assess knowledge beyond what is required. For me, if material is required learning, I want assess to what degree the students have learned, so I personnaly do not give extra credit. However, an essay type question on a more difficult topic when the test is mutiple choice (either electronic or scan-tron) has offered a way to earn 2-5 "bonus points". Out of of 125-150 points, that doesn't help a lot. but does reward those who attempt it, and in the big final grade, does not distort… >>>