The 2001 renewal of the United States' Title I program instituted the Supplemental Educational Services (SES) program, in which schools in their third year of failing to make Adequate Yearly Progress (AYP) are required to offer out-of-school-time tutoring in core subjects to low-income students. This study synthesized provider effects reported in the extant body of SES provider evaluations to generate an estimate of the overall effectiveness of the SES policy in terms of improving student achievement and to identify provider characteristics that are associated with variation in student achievement effects. (Contains 5 figures.)