The paper reports an evaluation of the introduction of a school-based assessment component into the 1986 NSW Higher School Certificate. A research team from Macquarie University and the University of Sydney monitored the processes of assessment policy development in eight Sydney schools during 1985 and 1986. These case studies of process and product were supplemented in 1986 by studies in ten NSW country high schools. A survey of teachers and students in a random sample of 58 high schools in NSW was completed towards the end of 1986. The results of the case studies and the survey are discussed within the following framework: Information Flow from the Board of Senior School Studies to the Schools; Policy Development in Schools; Features of Assessment Policies and their Implementation; and the Impact of Assessment on Classroom Practices and Relationships in the Classroom.