When I took math in elementary school, in the 80s, it was self paced. You really didn't get an F, you just kept studying a topic until you could pass it at 90%. On the other side, if you could pass a pre-test, you could skip the topic. It really enjoyed, because I could learn some topics in an hour, which would normally be 10 hours of boring instruction.

It was a little more work for the teachers, since the system admitted that kids were at a variety of levels, but it was roughly a normal distribution, where a whole classroom of kids were on normal pace, some were a little bit ahead or behind, and a few were way ahead or behind. It seems like adaptive learning software could make this even easier.