Most students took about 10 minutes; the longest was 15 minutes. Three students had been absent on Monday and Tuesday, so they studied alone while their peers took the quiz. They took the quiz one day later. I don't care if their friends told them about the questions -- they already knew!!
These questions are low-level on the classic Bloom's taxonomy, but that's OK. They are entry-level concepts to this month's unit about growth and change in the 1800s, and we applied these details in a terrific discussion later in that week.
The next day I return everyone's quiz sheet. A few students can see they have 1 or more concepts to review, because I circled them on the quiz. Those retakes require even less time than the initial quiz (unless they were totally unprepared on quiz day). Students sometimes take class time, or homeroom, or visit after-school to get them done. Occasionally I let them tell me the answer aloud without needing to write it down. Why do they go through this trouble?!
Because even if just one question was wrong, the score is 50%!! I know that's harsh, and it's supposed to be. We refuse to accept failure in my classroom, and students know that 50% can and should be replaced. (Here is where my "growth mindset" philosophy takes over...) Very very few students this year have let a 50% remain in the gradebook.
A revised quiz gets an official score of 85%. If someone needs a second chance at revision, then the score is 70%. [EDIT: In the 2015-16 school year, I changed the revised score to 90%, and second chances earn 80%. Those numbers seem a bit more realistic and fair, but I still grapple with the concept in the next sentence -->] I know you could argue that there should be no grade penalty for revisions, but I have learned the hard way that you need some "teeth" in the policy or else what's the point in trying the first time?
Please let me know what you think of this system. Am I a monster for giving failing grades when 80% of the quiz was correct? Did I skip an important step in my description?