drop out as measure

http://www.npr.org/2011/07/28/138750527/why-dropout-data-can-be-so-unreliable?ft=1&f=1013

darn -i thought it was going to say something about dropout rates not being a legit form of measurement of success..
why is dropping out of school a non-questioned standard of measure... perhaps a better question... what's so restrictive of schools that so many drop out...
not that schools are bad, just too restrictive.. that can be changed..