Three major national longitudinal studies have been conducted in Great Britain, each based on a week's births in, respectively, 1946, 1958, and 1970. This paper focuses on the implications for educators of the findings of the 1958 study, which examined the development, over 23 years, of approximately 5,000 children born in Britain in one week of 1958. Originally intended as a health-oriented study, the cohort also examined the educational and social characteristics and progress of its subjects and the interrelationships among these different aspects of their lives. One of the most important characteristics of the study has been its ability to study various kinds of change: in patterns of relative attainment in school, for example; in the effects of changing schools upon a child's educational development; or in the effects of other phenomena, such as test score placement, upon pupils' development. Even more importantly, the study has changed the researchers' own stereotyped perceptions of the nature of children and childhood. Several problems of large-scale longitudinal studies must be acknowledged, however, including compromising long-term goals to satisfy funding agencies' wishes for short-term results, lack of sufficient collaboration between the studies, and underexploitation of data. A list of 13 references is appended. (IW)