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 cultures that help teachers and students reach greater heights. What are they doing differently? The short answer is that greenhouse schools accomplish what others only claim to do; they prioritize great teaching above all else. That's TNTP's conclusion after surveying more than 4,800 teachers in almost 250 schools across the country over the past two years. Although other surveys have helped describe certain elements of school culture, TNTP researchers focused on two questions that they felt had not yet been answered: (1) What kind of school culture is most likely to increase retention of the best teachers and improve student learning?; and (2) What concrete steps can principals take to create that culture in their own schools? This executive summary presents five findings of this research: (1) Teachers want schools with a strong instructional culture--a culture that fosters great teaching; (2) Schools with strong instructional cultures retain more of their top teachers; (3) Schools with strong instructional cultures help students learn more; (4) A stronger instructional culture is within reach of any committed school leader; and (5) Dramatic improvements in instructional culture are possible--sometimes in just one year. [For the full report "Greenhouse Schools: How Schools Can Build Cultures Where Teachers and Students Thrive," see ED533216.]