This book describes recent psychological theories on the nature of intelligence and the influence of environmental factors, and argues that culture and child rearing practices affect the development of abilities (linguistic, sensory motor and perceptual). Studies of intelligence, achievement, and environment in England are discussed, along with those of immigrant groups in the United States, particularly of the Negro. The book attempts to show how cultural and educational influences in Jamaica, in East Africa, and among Indians and Eskimos in Canada affect the development of various abilities. Results of psychological and educational tests are incorporated in the argument presented which also treats the problems of testing "disadvantaged" children or adults in the developing countries. The purpose is to discover the reasons for low achievements and abilities in both developed and developing countries and to suggest, through these psychological investigations, what steps should be taken for remediation. (KG)