There is growing concern that improving the academic skills of children in poverty is too difficult and costly once they reach adolescence, and so policymakers should instead focus either on vocationally oriented instruction or else on early childhood education. Yet this conclusion might be premature given that so few previous interventions have targeted a key barrier to school success: ‘mismatch’ between what schools deliver and the needs of youth, particularly those far behind grade level. The researchers report on a randomized controlled trial of a school-based intervention that provides disadvantaged youth with intensive individualized academic instruction. The study sample consists of 2,718 male ninth and tenth graders in 12 public high schools on the south and west sides of Chicago, of whom 95 percent are either black or Hispanic and more than 90 percent are free- or reduced-price lunch eligible. Participation increased math achievement test scores by 0.19 to 0.31 standard deviations (SD)-depending on how the researchers standardized-increased math grades by 0.50 SD, and reduced course failures in math by one-half, in addition to reducing failures in nonmath courses. While some questions remain, these impacts on a per-dollar basis-with a cost per participant of around $3,800, or $2,500 if delivered at larger scale-are as large as those of almost any other educational intervention whose effectiveness has been rigorously studied.