I thought it said something about the powerlessness of kids against adults, even adults who are wrong. Another adult would never have put up with that jerk of a teacher.

Well, things were not good at Jake's home and we all know that this carries over into other areas of your life. He was angry, sad and felt hopeless about what was going on with his mother and Sam. I interpreted that scene as Jake just being fed up with everything and that teacher just happened to be the one to get it because he was such a royal jerk.

As a teacher, I will say this one is a real jerk. However, the scene when Jake blows up at him was the wrong course of action. He should have waited after class. However, the point of the scene was to show the frustration he had with all the dead ends of getting help.

The teacher was obviously a douche, but yes, I think Jake's troubles and frustrations at home and with Sam obviously exacerbated the problems with his teacher. Not sure if the teacher ever let him back into his class!
And he probably did plagarize just so he could get the report done