This is a relatively new concept to me... Do I understand it correctly, now in school, you get to take a test, and if you're not satisfied with your grade, you have the option of retaking the test? This is how my DD and DS have explained it to me. WTF?! You get a redo? If this were around 40 years ago I'd have had NO problem with school.
IKR?! I think a lot of teachers agree with your sentiment, but it's the district policy to allow students to retake a failed test for a maximum grade of a 70 (although there are some tests that are an exception to this rule). So to a point, it is okay because they can't retake it to replace with an A...especially if they failed to study for the test the first time, and thus having more time to study later (procrastination being reinforced, right? Sigh) and make a very high grade. But yeah, I still don't agree with being allowed to retake it. Asking for extra credit work is the best route, IMO...this is something that teachers rarely give or allow. I don't get that either.
Oh and our district has something called "grade repair"...if you have a 70 or below in a class, you go to tutorials to get help. I don't know how that works (nor do I wish to...but unfortunately, I think I will learn when my son hits high school next year LOL). Somehow, this will help you "repair" your failing grade.
Bottom line is - you will end up doing extra work/wasting MORE time repairing your failing grade than you would if you actually did the work/study the first time around!! Who'd have thought of that?!