School districts are spending millions on tutoring outside regular school day hours for economically and academically disadvantaged students in need of extra academic assistance. Under No Child Left Behind (NCLB), parents of children in persistently low-performing schools were allowed to choose their child's tutoring provider, and together with school districts, they were also primarily responsible for holding providers in the private market accountable for performance. We present results from a multisite, mixed-method longitudinal study of the impact of out-of-school time (OST) tutoring on student reading and mathematics achievement that link provider attributes and policy and program administration variables to tutoring program effectiveness. We find that many students are not getting enough hours of high-quality, differentiated instruction to produce significant gains in their learning, in part because of high hourly rates charged by providers for tutoring. We identify strategies and policy levers that school districts can use to improve OST tutoring policy design and launch improved programs as waivers from NCLB are granted.