In this study we revisit the impact of conditional cash transfers (CCTs) on child development, with an emphasis on the role of the age of exposure. We use longitudinal data from a unique paired-siblings sample of Peruvian children (the Young Lives study) to evaluate whether Juntos, a large-scale CCT implemented in Peru since 2005, has a greater effect on children who benefited from the programme during the first three years of life compared with its impact on those children who benefited between the ages of 5 and 7. To deal with programme selection we apply child fixed-effects methods. We find that exposure to the programme leads to a reduction in severe stunting and an improvement in height-for-age – but only for those exposed during the first three years of life. This result suggests that timing of exposure matters. However, no cognitive impact (as measured by a vocabulary-developmen...