[T-R]

That could be true, or it could not be. I had more courses before my OS class, but strictly speaking, I didn't necessarily need to take them in that order.

Either way, it seems that the thing to do would be to get more practice independently. If you're really worried about that particular course, see if you can read up on some of the material beforehand. If the assignments are published somewhere publicly, you could even start on them early.

Also, dropping the course and re-taking it isn't really a dirty trick - they just took some more time to learn the material. You could do the same by getting a head start practicing it. If they finished with a 96% the second time, there's a good chance they learned more from it than someone who got through with a 50% and never touched the material again.