This study applies a bioecological lens to the examination of school change in the area of classroom assessment. We conducted a case study that examined the processes within a rural secondary school that supported and inhibited change in classroom assessment practices. Data collection included teacher and principal interviews, focus groups, document analysis of teacher unit plans, and classroom observations. The bioecological lens revealed that the principal was key to establishing proximal processes that supported change and that teacher micro-systems and larger exosystem factors both supported and inhibited growth, often creating buffers for teachers against exosystem pressures.