Children from low-income families are at risk of learning outcome difficulties, particularly in literacy. Various studies link poor literacy results with performance later in primary and secondary school, and suggest that poverty, literacy skills and weak instructional methods combine to drastically limit the educational opportunities for many poor children. The Primary Math and Reading (PRIMR) Initiative was designed to support the learning gains of Class 1 and 2 pupils in seven counties across Kenya. PRIMR uses a randomised controlled trial design to establish the effect of its intervention and employs basic literacy measures to estimate causal effects. This study shows that PRIMR has been effective for children from low-income families and that early literacy interventions can mitigate socio-economic effects. The findings suggest that efforts to improve literacy outcomes for the poor should begin early in primary school. Strategies for ensuring that instruction is equitable across socio-economic status are advocated.