Bottom quartile pilots

Random thought of the day: every fourth time you get on an airplane, the pilot is a bottom quartile pilot.  Why doesn't that cause me angst, whereas I'd NEVER want one of my children in a classroom with a bottom quartile teacher?  The answer is simple: because we have a system for training and evaluating pilots and weeding out the bad ones that ensures that even the bottom quartile are highly competent.  So why don't we have a similar system for teachers?!?!