Journal article: This paper provides new evidence of sharp differences in cognitive development by socioeconomic status in early childhood for five Latin American countries using a common measure of receptive language ability. We find important differences in development in early childhood across countries and steep socioeconomic gradients within every country. For the three countries where we can follow children over time, there are few substantive changes in scores once children enter school. Our results are robust to different ways of defining socioeconomic status, to different ways of standardizing outcomes, and to selective nonresponse on our measure of cognitive development.