Research has been showing that the most important development in K-12 education over the past decade has been the emergence of a growing number of urban schools that have been convincingly shown to have dramatic positive effects on the achievement of disadvantaged students. Those with the strongest evidence of success are oversubscribed charter schools. These schools hold admissions lotteries, which enable researchers to compare the subsequent test-score performance of students who enroll to that of similar students not given the same opportunity. Through careful study of the most effective of these charter schools, researchers have identified common practices--a longer school day and year, regular coaching to improve teacher performance, routine use of data to inform instruction, a culture of high expectations--that have yielded promising results when replicated in district schools.