Schools that have not made adequate yearly progress in increasing student academic achievement are required, under No Child Left Behind (NCLB), to offer children in low-income families the opportunity to receive supplemental educational services (SES). In research conducted in Milwaukee Public Schools, the authors explore whether parents and students are aware of their eligibility and options for extra tutoring under NCLB, and who among eligible students registers for SES. Using the best information available to school districts, the authors estimate the effects of SES in increasing students' reading and math achievement. They find no average impacts of SES attendance on student achievement gains and use qualitative research to explore possible explanations for the lack of observed effects. Appendices include: (1) Supplemental Education Services Evaluation Focus Group Protocol; and (2) Milwaukee Public Schools 2006-2007 Supplemental Education Services Student Survey. (Contains 8 tables and 19 notes.) [This paper was presented at the "NCLB: Emerging Findings Research Conference" at the Urban Institute, Washington, D.C. on August 12, 2009.]