Family and school influences on cognitive development are reviewed in terms of the empirical research findings on (i) variations within the ordinary environment; (ii) family intervention studies; (iii) the effects of abnormal environments; (iv) extreme environmental conditions; (v) variations within the ordinary school environment; and (vi) preschool and school intervention studies. It is concluded that environmental effects on IQ are relatively modest within the normal range of environments, but that the effects of markedly disadvantageous circumstances are very substantial. Cognitive development is influenced both by direct effects on cognition and by indirect effects through alterations in self-concept, aspirations, attitudes to learning and styles of interaction with other people.