This paper presents results from a large-scale randomized evaluation of the One Laptop per Child program, using data collected after 15 months of implementation in 318 primary schools in rural Peru. The program increased the ratio of computers per student from 0.12 to 1.18 in treatment schools. This expansion in access translated into substantial increases in use of computers both at school and at home. No evidence is found of effects on test scores in math and language. There is some evidence, though inconclusive, about positive effects on general cognitive skills.