Smiling politely through yet another performance by my son's school band tonight, I wondered: why do school bands play music so different from what the kids, or even their parents, choose in their free time?  Music at parties, movies, etc. is pretty different.  The novels kids read in English class differ from the novels they or their parents read in their free time, but most people accept that school novels are deeper, subtler, etc., so that kids learn more by studying them.  But do most people really accept a similar claim about band music?  What gives?

Added: There are lots of high quality thoughtful comments here.  So is there a disagreement here, or do you guys pretty much agree?