There are substantial learning gaps across countries on standardised international assessments. In this paper, I use unique child-level panel data from Ethiopia, India, Peru and Vietnam with identical tests administered across these countries to children at 5, 8, 12 and 15 years of age to ask at what ages do gaps between different populations emerge, how they increase or decline over time, and what the proximate determinants of this divergence are.

I document that a clear pattern of stochastic dominance is evident at the age of 5 years, prior to school enrolment, with children in Vietnam at the upper end, children in Ethiopia at the lower, and with Peru and India in between. Differences between country samples grow in magnitude at later ages, preserving the country rankings noted at 5 years of age over the entire age range studied. This divergence is only partly explained by home investments and child-specific endowments in a value-added production function approach. The divergence in achievement between Vietnam and the other countries at primary school age is largely explained by the differential productivity of a year of schooling. These findings are confirmed also using an instrumental variables approach, using discontinuities in grade completion arising between children born in adjacent months due to country-specific enrolment guidelines.