Having a husband who was labeled as a discipline problem right before he was labeled about 6 grades ahead of his current grade level, and having had a brother who's incredibly smart and talented and also at various turns of his academic career a discipline problem, sometimes a child can become a discipline problem merely because a teacher has no idea what to do with the kid, especially when the kid in question is

(a) smart enough to know more than you do but not socially savvy enough to keep it under wraps so as to not antagonize their teacher (my husband)
(b) smart enough to figure out exactly what shortcoming a teacher is covering up by belittling other kids, and yet not mature enough to realize that paying a bully teacher in kind with snide remarks is not going to be an engagement on a level playfield (my brother).

Happens more often than you'd think, especially to boys (smart girls are better able to just keep their mouth shut, in my personal experience).