Our objectives were to document and examine socioeconomic gradients across a comprehensive set of child development measures in a population living in extreme poverty, and to interpret these gradients in light of findings from the neuroscience literature. We assessed a nationally representative sample of 3–6-year-old children (n = 1332) from 150 communities of Madagascar using standard tests of development. We found that children whose families were in the top wealth quintile or whose mothers had secondary education performed significantly better across almost all measures of cognitive and language development and had better linear growth compared with children of women in the lowest wealth quintile or women with no education. These differences between children of low and high socioeconomic position were greatest for receptive language, working memory, and memory of phrases. The mean difference in the scores between children in the highest and lowest socioeconomic status categories doubled between age 3 and age 6, and the biggest gaps across socioeconomic position by age 6 were in receptive language and sustained attention. Our results suggest that even within the context of extreme poverty, there are strong associations between family socioeconomic status and child development outcomes among preschool children, and that the language and executive function domains exhibit the largest gradients.