This paper compares and contrasts three groups that conducted biological research at Yale University during overlapping periods between 1910 and 1970. Yale University proved important as a site for this research. The leaders of these groups were Ross Granville Harrison, Grace E. Pickford, and G. Evelyn Hutchinson, and their members included both graduate students and more experienced scientists. All produced innovative research, including the opening of new subfields in embryology, endocrinology and ecology respectively, over a long period of time. Harrison's is shown to have been a classic research school; Pickford's and Hutchinson's were not. Pickford's group was successful in spite of her lack of department or institutional position or power. Hutchinson and his graduate and post-graduate students were extremely productive but in diverse areas of ecology. His group did not have one focused area of research or use one set of research tools. The paper concludes that new models for research groups are needed, especially for those, like Hutchinson's, that included much field research.