Right, it's both.

When I was in high school, I got a lot of Bs and Cs -- not because I didn't understand the material, but because the homework was so uninteresting that I didn't bother to do it. I slept through most of my classes -- they were slow enough that I didn't need to be awake, and the more sleep I got at school, the less sleep I needed at home, and the more free time I got -- so I got bad participation grades.

And then there was an AP Computer Science class I took, taught by a business teacher drafted into it by the administration. She didn't know the first thing about the material, so I got points docked for doing things she didn't understand, points docked for correcting her errors on the tests, points docked for going on IRC instead of listening to her lecture incoherently on things I already knew... and I had friends in the class who were in the exact same situation. She eventually cooked up some ridiculous scheme to try to get us all expelled: she falsely accused us of running a credit card fraud ring. And it worked.