Researchers studied Zambia's Teaching at the Right Level program, delivered by government teachers nationwide, using a pre-registered cluster-randomized trial and an event study covering 4.4 million exam scores. After two years, the program improved children’s foundational literacy and numeracy. Gains in mathematics were concentrated in the procedural skills the program targets, with near-zero improvement in other competencies. Yet by the end of primary school, cohorts exposed to the program scored higher on comprehensive leaving exams in both subjects. This contrast suggests that the broader returns to targeting foundational skills can operate over longer horizons.