Quote from a friend:

A great quote from a friend who relatively new to this issue and just learned the details of our insane teacher tenure system: "If you want to guarantee poor performance, then set up a system that gives people a job for life regardless of performance."  (Of course teachers should have protections against arbitrary, discriminatory, and/or capricious termination, but the current system goes FAR, FAR beyond that, entrenching mediocrity (or far worse) – and, of course, completely screwing kids.)