Kendallina....you're right, it does seem very common....to me, it seems especially common here and it's saddening in some cases. I fear we are doing a huge disservice to children when we just "pass the buck" because of behavior issues. It only prolongs and perpetuates the problem for the child.
Anyways, it is more common than many realize, there was a study done on this and it is actually much more frequent in private programs than in state-funded. Here is a link:
http://www.ncpa.org/sub/dpd/index.php?Article_ID=2290