Whether targeted foundational instruction yields broad, long-term human capital gains is central to education policy but largely untested. We provide causal evidence from Zambia’s government-run foundational skills program in public primary schools. After two years, a randomized trial shows the program increases literacy by 0.10 and numeracy by 0.15 standard deviations. In mathematics, effects on targeted skills are 2.6 times larger than on comprehensive assessments, without detectable transfer to adjacent domains. Adding professional development doubles per-pupil costs without additional learning gains. Despite limited short-run transfer, event-study estimates show positive effects on grade-7 language and mathematics exam scores in early adolescence.