This co-authored book is based upon a four year study of variations in teachers' work and lives and their effects on pupils. It involved three hundred teachers of different age and experience, working in one hundred primary and secondary schools of different socio-economic status in England. The study is the first and largest of its kind. Qualitative and quantitative data were collected from the teachers, heads and pupils (including test results at key stage 1, 2 and 3, English and Maths) over a three year period. These concerned the impact on teachers' lives and work related to their own histories and to that of colleagues of similar experience working in similar contexts. Different patterns of influence and effect were identified between groups of teachers which provide powerful evidence of the contextual complexities of teachers' work, lives, identities and commitment in relation to agency, well-being, resilience and the associations between these and pupil attitudes and attainment. These have clear messages for policy makers, school leaders, teachers' associations and teachers themselves in understanding, supporting and sustaining their capacities to build and sustain classroom effectiveness.This distillation of the work presents those findings of the study which will be of direct interest to policy makers, teachers' associations and had teachers not only in the UK but also internationally. The book highlights the importance of career and professional development, the positive and negative influences upon these, the relationship between school leadership, culture and teachers' lives and how these relate to effectiveness. The work is original and highly relevant, since its messages relate directly to teacher recruitment and retention and the work-life balance, well-being and effectiveness agendas.