This dissertation presents the results of three field experiments implemented to evaluate the effectiveness of strategies to improve the health or education of children in developing countries. In Guatemala, community health workers at randomly selected clinics were given patient tracking lists to improve their ability to remind parents when their children were due for a vaccine; this is found to significantly increase children's likelihood of having all recommended vaccines. This strategy is particularly effective for older children. In Peru, a teacher training program is found to have no effect on how frequently children use their computers through the One Laptop Per Child program. In Costa Rica, learning English as a foreign language using one software program is found to be significantly more effective than studying with a teacher, or with a different software program, confirming the heterogeneity of effects of educational technology.