This longitudinal multiple methods study used an ethnographic approach to examine the development of early adolescents' psychology during pubertal and school transitions. It explored potential associations between attitudes to school, perceptions of school life and transfer, home and peer relations, and puberty over the course of a school year. It compared two groups of UK 11 and 12 year olds (Year 7), one in a middle school (age range 8-13 years) without transfer at age 11, and the other in a secondary school (11-16 years) where transfer from primary school had just occurred. Pupil attitudes to school were surveyed across the Year 7 cohort in each school at the beginning (N=252) and end (N=262) of the school year. The initial survey facilitated selection of two matched groups of target pupils (N=20) who were engaged in an active participation method designed to improve validity. Data on perceptions of school and growing up were gathered in 80 interviews, 40 audio diaries, 42 hours of participant observation and by 63 targeted observations across three school terms. An end of year survey assessed the attitudes of the target pupils and their year groups. Qualitative data were analysed inductively using grounded theory coding procedures which uncovered early adolescent needs that mismatched with many design features of secondary schooling. Of particular developmental offence were impersonal teachers and lessons that were non-practical, without opportunity for independent learning and unsupervised skills building and that were irrelevant to adolescents' career identities. Analysis of the quantitative survey data using multivariate procedures identified attitudinal factors congruent with previous research. Overall attitude to school was best predicted by perceptions of teachers and enjoyment of lessons rather than by adolescent developmental factors. Cluster analysis identified four pupil types validated by the target pupil findings. Of these the autonomy seekers had the most freedom outside of school and the greatest decline in attitudes across the year. The findings assisted generation of new theory incorporating concepts of maturity status markers and focal contexts. School transfer was found to impel an ecological transition across multiple developmental contexts which increased pupils' maturity self-perceptions, yielding mixed developmental implications. Using Bronfenbrenner's (1979) ecological systems framework as an analytical tool facilitated interpretation of the emergent themes in relation to Eccles & Midgley's (1989) US-based theory of 'Stage-Environment Fit'. The findings support the application of a modified Stage-Environment Fit theory in English schools.