This project sets out to test extensively a number of different developmental measures on a large sample of children in a specific context in Latin America. There are two aims and objectives of this study. First, we want to provide a validation of a number of tests commonly used in the literature. By correlating the short and easy to administer measures with the results obtained with a longer, high quality test we can check which of the short tests better approximate the standardized long test. Second, we will also provide a comprehensive developmental profile of the cognitive, language, motor and socio-emotional development of a cohort of children in a specific context of Latin America. Such diagnostics would certainly be useful in planning, designing and evaluating policy interventions and in educational, psychological, and economic research studies. We will measure poor and middle class children at different ages, so that we will be able to measure the socio-economic gradient in cognitive (and non-cognitive) development from 6 to 42 months of age. This project will address a real demand to establish the validity and reliability of short tests. This will have important implications as it will determine which (if any) of the short tests can be confidently used in large scale projects. There is an increasing demand for such low cost measures within the evaluations of new interventions aimed at the mental and motor development of young children.