When a class as a whole does not do as well as expected on a test, I give a retest. The retest is shorter and easier than the original test because I simply modify some of the material that was in the original test. I then average the two grades to get the students' grade for that test. If a student gets a 60% on the first test, and a 100% on the second test, his/her grade for that test would be 80%. If a student gets a worse grade on the retest than on the first test, then the retest is not counted. There is no penalty for taking a retest. Retests are optional, and all students are eligible. I have had students who got a 96% on the first test choose to take a retest, and students who got a 40% on the first test choose not to take a retest In this way, students who did well on the first test still do better than the others who did not do so well.