Pretty much all of my sixth grade teachers (aside from the art teacher, who was pretty cool) were horrible, as were the students. Sixth grade quite honestly remains one of the lowest points in my life to date.
Ironically, most of the rest of my school experience has been pretty good, with the exception of the art teachers. I had one in eighth grade who was incredibly condescending to several of the students including myself, and frequently gave preferential treatment to subpar works simply because they followed the directions more closely.
The art teacher I had from ninth all the way through twelfth grade (She and the TA were the entire art department at the high school) wasn't nearly as bad (and in fact I have to admit that she's a major factor in my present art skills being halfway decent) but there were several times when she and I butted heads over how I did my shading.