For researchers seeking to improve education, a common goal is to identify teaching practices that have causal benefits in classroom settings. To test whether an instructional practice exerts a causal influence on an outcome measure, the most straightforward and compelling method is to conduct an experiment. While experimentation is common in…

This paper reviews research on the design and effectiveness of preschools in the United States. Three randomized controlled trials that enrolled roughly 350 total children in demonstration studies during the 1960s and 1970s shape much of the current discussion of preschool. We examine what these studies and more recent ones based on random…