The supplemental educational services (SES) provision of No Child Left Behind introduces a federally mandated after-school tutoring intervention in schools that fail to make adequate yearly progress. This article examines market dynamics in relationship to the law's goals of expanding access to and improving the quality of after-school programming. Analysis of operational and financial data from seven SES providers suggest that relative to smaller local firms, national firms are positioned to capture more of the SES market. Analysis of data on SES provider activity (from 2004 to 2006) within an urban district suggests that firms gaining market share charge higher hourly rates and have larger class sizes. Survey data from 30 state administrators reveal the limited capacity of states to monitor providers. This analysis points to a mismatch between the implementation of SES and the concerns for quality and equity that are claimed as priorities within federal law. (Contains 4 tables and 12 notes.)