“[E]arly, and effectively irreversible, decisions about teacher tenure have real costs for students and ultimately all of society.

Teacher tenure, and the related onerous and costly requirements for dismissing an ineffective teacher, have evolved into a system that almost completely insulates teachers from review, evaluation, or personnel decisions that would threaten their lifetime employment. Research shows that this results in serious harm both to individual students and to society, because a small number of grossly ineffective teachers are retained in our schools.”