Undertaken by the ASER Center of Pratham, this study explores a set of interrelated factors that influence how teachers teach. Designed as a series of data collection exercises that were conducted between July 2013 and December 2014, the study covered 400 schools and tracked more than 2,200 teachers during visits to each school. The study uses teacher surveys and classroom and school observations methods. It evaluates teachers' subject-matter knowledge, ability to communicate, and ability to learn from children's work. The findings generated by the study provide significant inputs and suggestions for designing future teacher training and teacher professional development programs.