To give a mark of zero on a quiz or homework assignment means that the student knows nothing at all. In 99.9% of cases even if an assignment is not turned in, the student knows more than zero. For that reason , I can not give a zero!
After the test occurs, we have a pretty good idea as to what the student knows even if nothing is turned in. All HW and 100% quizzes that are not turned in before the test day will be replaced by the known test or retest score.
A better retest will raise any marks that were previously created using the first test's percentage.
Students who complete all their HW and do all their corrections on review materials and 100% achieve higher scores than those that do not. In 90% of cases, I strongly urge students to complete and correct every question assigned.