The purpose of the three-year Cooperative Language Development Project was to examine the efficacy of an oral language development program and an experimental reading program in improving the academic achievement, language development, intellectual functioning, and creative thinking of disadvantaged children in primary grades. The experimental treatments were: (1) an oral language program consisting of experimental versions of the Peabody Language Development Kits, and (2) an experimental reading (Initial Teaching Alphabet) approach. In contrast to the experimental groups, a control group used a conventional basal reading program. The effectiveness of the experimental programs was measured by various standardized tests, such as the Peabody Language Production Inventory and the Stanford-Binet Intelligence Scale. After three years of intervention, the two experimental approaches in combination appeared to be most effective treatment for improving the intellectual and language development as well as the school achievement and creative thinking of disadvantaged children. It appears that exposure to the experimental reading and language development programs in this study had a number of beneficial effects. [For a report of the Project "after two years," see ED 026 125.] (Author/JW)