"Evaluation Science Briefs" summarize the findings and implications of a recent study evaluating the effects of an early childhood program or environment. This Brief evaluates the study "An Effectiveness-Based Evaluation of Five State Pre-Kindergarten Programs" (V. C. Wong, T. D. Cook, W. S. Barnett, and K. Jung.) States have high aspirations for the investments they are making in pre-K education. Findings from this study indicate that these hopes are largely justified, although the evidence does not yet explain why some programs are more successful than others.