@redsad
Ha. I figured that out in middle school, and stopped doing homework.
I never failed a class, but I made a lot of teachers VERY angry at me. My response was simple: if I knew the material, doing a bunch of busy work was pointless. And they could NEVER prove I didn't know it, because I did.
I'm an advocate of doing enough work to be certain you understand the concept, and then stopping.
If I had kids, their teachers would hate me.