The study is an investigation of unplanned change initiated by teachers in the physical education department of Forest School, an Upper School and Community College in England. The events at Forest are conceptualised as a case of teacher-initiated innovation. The study draws on interviews with teachers, observations of lessons and analysis of curriculum documents in the collection of data. Three issuesýprovide foci for the study. First, the study investigates the temporal dimensions of innovating, and reveals that the innovative idea of health related fitness based physical education became formalised and objectified over time. This process of formalisation had important implications for the second area of focus, the teachers' involvements in the innovative process. While each of the physical education teachers played important roles in the implementation of the innovative idea, each participated in the innovation with varying degrees of involvement, and held disparate conceptions of the innovative idea and of its implication for practice. Third, the study locates and attempts to understand the process of innovating in the work context of teaching. The teachers at Forest saw innovating and teaching as synonymous activities, and the study documents the extent to which the innovative situation exacerbated teachers' everyday preoccupations with success, reward and students. The study provides information on the dynamics of unplanned educational change and the findings lend qualified support to the trend towards school-centred innovation.