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. In high school, the estimated gains are somewhat smaller than in middle school: .16 to .19 standard deviations in English Language Arts; .16 to .19 in mathematics; .2 to .28 in writing topic development; and .13 to .17 in writing composition with the lottery-based results. The estimated impacts of middle schools and high school Charters are similar in both the “observational” and “lottery-based” results.