Fifteen years ago, lawmakers in Massachusetts sponsored a bold experiment designed to answer this question: If public schools were granted more autonomy to staff their own classrooms, choose their own curricula and manage their own budgets, could they deliver improved student achievement? The presentation focuses on two distinct research designs: an observational study and a lottery study. Together they provide a comprehensive analysis of student achievement in Boston's public schools, including Pilots and Charters. Whether using the randomized lotteries or statistical controls for measured background characteristics, we generally find large positive effects for Charter Schools, at both the middle school and high school levels. For each year of attendance in middle school, we estimate that Charter Schools raise student achievement .09 to .17 standard deviations in English Language Arts and .18 to .54 standard deviations in math relative to those attending traditional schools in the Boston Public Schools. The estimated impact on math achievement for Charter middle schools is extraordinarily large. Increasing performance by .5 standard deviations is the same as moving from the 50th to the 69th percentile in student performance. This is roughly half the size of the blackwhite achievement gap.