Efforts to improve the educational achievement of children, especially those from disadvantaged backgrounds, are at the heart of current government policies in the United Kingdom. The Peers Early Education Partnership (PEEP) is an intervention that, since 1995, has worked directly with parents and caregivers of children from infancy to 5 years of age in a deprived area of Oxford and, recently, in other areas. This paper explores the effects of the PEEP parental education program on children's development. A longitudinal quasi­-experimental design, including pretest and post-test measures, was used to compare a group of children whose parents had access to PEEP with a group of children with similar demographic characteristics whose parents did not have such access. In order to assess the effects of PEEP on children's cognitive, language, and social-­emotional development, standardized tests and educational tasks were administered to the children upon entry to the intervention (at age 3) and after one and two years (at ages 4 and 5). This paper discusses the effects of two years of parental participation in PEEP on children (at age 5). Gains were found in vocabulary, verbal comprehension, understanding about books and print, number concepts, and self-­esteem related to both cognitive and physical competence. Thus, working directly through groups of parents was found to be an effective way of enhancing children's cognitive and social­-emotional development.