Professional development for teachers is regarded as one of the principal pathways through which we can understand and cultivate effective teaching and improve student outcomes. A critical component of studies that seek to improve teaching through professional development is the detailed assessment of the intermediate teacher development processes…

Like performance-enhancing drugs inflating apparent athletic achievements, several common social science practices contribute to the production of illusory results. In this article, we examine the processes that lead to illusory findings and describe their consequences. We borrow from an approach used increasingly by other disciplines--the norm of…

Multisite trials, in which individuals are randomly assigned to alternative treatment arms within sites, offer an excellent opportunity to estimate the cross-site average effect of treatment assignment (intent to treat or ITT) "and" the amount by which this impact varies across sites. Although both of these statistics are substantively…