The decline of child study coincided with the rapid transformation of psychology from a branch of philosophy into an independent science. In 1897 two psychology laboratories were established – one in Cambridge, one in University College, London – and in October 1901, the British Psychological Society was founded. In January 1904 James Ward and W. H. R. Rivers edited the first number of the British Journal of Psychology. They encouraged psychologists to abandon transcendental issues and speculative methods for empirical problems and scientific techniques, hoping to establish the new discipline in the scientific community. ‘In becoming a distinct science’, they argued, ‘it has thus increased the intimacy and variety of its connections with other sciences manifold.’ By 1914 there were eleven posts in psychology in various English and Scottish universities, as well as Cyril Burt's half-time job as official psychologist to the LCC. The technical literature on the discipline grew rapidly. In 1921 a separate British Journal of Medical Psychology was established; and in 1930 the BPS took over the Forum of Education and renamed it the British Journal of Educational Psychology.

Educational psychology was a prominent specialism within the expanding profession. The psychology of individual differences and the technology of mental measurement found their ideal subjects in the school population. School teachers learned a smattering of psychology in their teacher training courses. The LCC tried to solve some of the problems of classifying school children by employing an official psychologist. The school medical services increasingly turned to psychological theory for help in dealing with the mentally subnormal.