School districts required under No Child Left Behind (NCLB) to provide supplemental educational services (SES) to students in schools that are not making adequate yearly progress rely heavily on the private sector to offer choice in services. If the market does not drive out ineffective providers, students may not gain through SES participation. We estimate SES provider effects on students' math and reading achievement in an urban school district that accounts for a significant share of participating students. We expect this research to inform education policy on the viability of policy interventions employing a private market model to improve public sector outcomes, including the reauthorization of Title I and district tutoring interventions under NCLB and after federal waivers from NCLB.