The primary purpose of this toolkit isto provide a resource for researchers from variousdisciplines interested in planning and evaluating programsor interventions aimed at improving the health anddevelopment of infants and young children. The toolkit aimsto: provide an overview of issues affecting earlydevelopment and its measurement; discuss the types of teststypically used with children under five years; provideguidelines for selecting and adapting tests for use indeveloping countries, and make recommendations for planningsuccessful assessment strategies. The toolkit focuses onchildren who have not yet entered school, and are thus undersix years old. The primary reason we are focusing on thisage group is that during the first five years of life,children's language, early understanding of mathematicsand reading, and self-control emerge. The extent to whichchildren master these skills during this critical period hasimplications for success in school (Lerner, 1998), and thuswe wanted to focus on children in this pre-school period.The toolkit is essential at this time for the followingreasons: children in developing countries are growing up ata disadvantage; assessments of children must expand toinclude a wider range of outcomes; and no such toolkitexists as present.