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.
The authors used a random-assignment experiment in Los Angeles Unified School District to evaluate various non-experimental methods for estimating teacher effects on student test scores. Having estimated teacher effects during a pre-experimental period, they used these estimates to predict student achievement following random assignment of teachers to classrooms. While all of the teacher effect estimates considered were significant predictors of student achievement under random assignment, those that controlled for prior student test scores yielded unbiased predictions and those that further controlled for mean classroom characteristics yielded the best prediction accuracy. In both the experimental and non-experimental data, the authors found that teacher effects faded out by roughly 50 percent per year in the two years following teacher assignment.
The National Board for Professional Teaching Standards (NBPTS) assesses teaching practice based on videos and essays submitted by teachers. For this study, the authors compared the performance of classrooms of elementary students in Los Angeles randomly assigned to NBPTS applicants and to comparison teachers. The authors conclude that students assigned to highly-rated applicants outperformed those in the comparison classrooms by more than those assigned to poorly-rated teachers. Moreover, the estimates with and without random assignment were similar.