I use this product with my students daily, each student is responsible for tracking which subtraction test they are on (I have a included a checklist to keep track). Each day I have students come up and tell me which timed test they are on. I give the students two minutes to practice the problems on their own using the answer key to check their answers. Once the two minutes is up, students fold down the answer key and I give the students one minute to try to complete the whole worksheet. If students complete the entire worksheet they bring it to me, and I check their work (I write their score in the box on the bottom right hand corner). If they do not complete the entire worksheet they take the paper home and practice it for homework and try the same problems again tomorrow.
Another way you could use this product if you do not have time to use it daily is to do the timed test once a week, and instead of one minute to complete it, you can give the students two minutes.
I have included flash cards in this product to give to students to have them practice the facts they are on. At conferences I run copies of all of the flash cards to give to parents to help their students practice their facts.
My students love this product and I love the feeling of accomplishment they get when they pass their test.