In "The Irreplaceables," TNTP researchers argued that America's urban schools take a negligent approach to teacher retention, losing too many of their very best teachers--their "Irreplaceables"--and keeping too many of their weakest teachers, year after year. A combination of weak school leadership, poor working conditions and restrictive policies…

Successful teachers make successful schools. Yet some schools are better than others at accelerating student learning by developing and keeping great teachers, even compared to schools that serve the same population of students and have access to the same resources. These schools are called "greenhouse schools"--schools with carefully fostered…

Experience makes a difference--especially at the beginning of a teacher's career. On average, teachers with some experience are more effective than brand new teachers. Teachers improve the most early in their careers. One study found that "close to half of the teacher achievement returns to experience arise during the first few years of teaching."…