NBER Working Papers by Martin West

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Working Papers

December 2013Endogenous Stratification in Randomized Experiments
with Alberto Abadie, Matthew M. Chingos: w19742
Researchers and policy makers are often interested in estimating how treatments or policy interventions affect the outcomes of those most in need of help. This concern has motivated the increasingly common practice of disaggregating experimental data by groups constructed on the basis of an index of baseline characteristics that predicts the values that individual outcomes would take on in the absence of the treatment. This article shows that substantial biases may arise in practice if the index is estimated, as is often the case, by regressing the outcome variable on baseline characteristics for the full sample of experimental controls. We analyze the behavior of leave-one-out and repeated split sample estimators and show that in realistic scenarios they have substantially lower biases th...
December 2011Does Practice-Based Teacher Preparation Increase Student Achievement? Early Evidence from the Boston Teacher Residency
with John P. Papay, Jon B. Fullerton, Thomas J. Kane: w17646
The Boston Teacher Residency is an innovative practice-based preparation program in which candidates work alongside a mentor teacher for a year before becoming a teacher of record in Boston Public Schools. We find that BTR graduates are more racially diverse than other BPS novices, more likely to teach math and science, and more likely to remain teaching in the district through year five. Initially, BTR graduates for whom value-added performance data are available are no more effective at raising student test scores than other novice teachers in English language arts and less effective in math. The effectiveness of BTR graduates in math improves rapidly over time, however, such that by their fourth and fifth years they out-perform veteran teachers. Simulations of the program’s overall impa...
May 2008The Non-Cognitive Returns to Class Size
with Thomas Dee: w13994
Although recent evidence suggests that non-cognitive skills such as engagement matter for academic and economic success, there is little evidence on how key educational inputs affect the development of these skills. We present a re-analysis of follow-up data from the Project STAR class-size experiment and find evidence that early-grade class-size reductions did improve subsequent student initiative. However, these effects did not persist into the 8th grade. Furthermore, the external and, possibly, the internal validity of these inferences is compromised by non-random attrition. We also present a complementary analysis based on nationally representative survey data and a research design that relies on contemporaneous within-student and within-teacher comparisons across two academic subjects...

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