This study investigated the effect of preschool experience (two types of preschool: Madrasa and non-Madrasa) on the cognitive development of children in East Africa. In the three countries studied (Kenya, Uganda, and Tanzania/Zanzibar) preschool education is burgeoning and government standards are being set. This quasi experimental evaluation used four subscales (block building, verbal comprehension, early number concept, picture similarities) adapted from the British Ability Scale II (BAS II; discussed by Elliot, Smith and McCulloch in 1996), and three (verbal meaning, exclusion, closure) from the African Child Intelligence Test (ACIT; discussed by Drenth and colleagues in 1980). The development of 423 children was studied at pre-test (entry to preschool) and at post-test 18 months later. Hierarchical regression showed that children with both types of preschool experience performed better than the home (comparison) group; however, children attending Madrasa Resource Centre preschools achieved significantly higher scores overall. (Contains 6 tables.)