Head Start is a federal early childhood intervention designed to reduce disparities in preschool outcomes. The first randomized experimental study of Head Start, the National Head Start Impact Study (NHSIS), found impacts on academic outcomes of .15 to .3 standard deviations measured at the end of the program year, although the estimated impacts were no longer significant when measured at the end of kindergarten or first grade. Assessments that Head Start is ineffective based on the NHSIS results are in our view premature, given our currently limited understanding of how and why early childhood education improves long-term life chances. Many of the specific changes to Head Start that have been proposed could potentially wind up doing more harm than good. (author abstract)