I've arranged for all 3 of my courses to have two chances to take the final exam. Most of my students will not benefit from this, because they try to cram too much into too little time. But some students will really solidify their understanding, and so it's worth it.
The final exam is one grade, but that's not how I do my other tests. Those are broken up into subtests, each on one topic. (See the example below.) The student gets a grade for each subtest, and I allow retakes of any subtest they didn't score well on. In Intermediate Algebra and Pre-calculus, they can come in whenever they want, show me that they've learned the material, and I'll make them a new version of the test (the whole thing, or just one or a few subtests).
I can't make new test versions so quickly in Calc II, so we work out a day that everyone who wants to retest can come. We scheduled a day this week or next for each of the previous tests. I hope this helps them!
The one new thing I've done this semester in relation to tests is to add a problem-solving subtest onto each test in Pre-calculus. My tests used to be way too hard, and I've made them easier over the years. I've worried that they were too easy (even though students don't do as well as I'd like). I want to test on their thinking skills. But I knew that was too stressful. This semester I came up with the idea of having one problem on each test that would require some real problem-solving. They only have to get this problem right once during the semester. There are still lots of students who haven't gotten one right, so during the final, I'll have a separate problem-solving test available, with 3 problems to choose from. Next semester I'll gather together the problems I've used this semester into a problem-solving handout, and we'll work more in class on how to problem solve.
My colleagues worry that doing this would take too much time. But I think I work less than they do, because they put more time into grading homework, and they probably agonize over partial credit like I used to. My tests are very short now, and both making and grading them is usually pretty quick.
I like seeing my students take more responsibility for their learning. It's really changing how some of them deal with math class. I know I have a long way to go to catch up with some of the people whose classes are blossoming with SBG; it's a great journey to be on.