One of the things that often happens is numerous people may want to use the scantron machine or copy machine at one time. To avoid waiting, I've made master copies of all the exams and look through them each time one is administered to ensure there's no writing on it. There are numerous forms of each exam.
As for scantrons, one method I've found works best is to simply punch holes as answers on the actual scantron key, and then place it over a student's scantron. Each hole that is unmarked is an incorrect answer.
