This report is one of a series that documents progress in understanding the effects of new assessment based on case studies in three elementary schools. It presents the preliminary analyses of interviews with teachers about their knowledge, beliefs, and practices related to assessment and instruction in reading and mathematics. Changes in beliefs and practices are also examined during a year-long intervention designed to help teachers develop performance assessments. Subjects were 3rd-grade teachers at three elementary schools who participated in weekly workshops in assessment development. It was clear from these preliminary findings that teachers added to their repertoires of assessment activities. In reading, they clearly considered these new activities--running records and written summaries--to be new forms of assessment, and they reported new insights about reading and student skills. In mathematics teachers did incorporate new activities, but only some of the teachers considered these activities to be assessment tools. Interview responses do not make clear the extent to which teachers are receiving new insight about student achievement from the new activities. End-of-year interviews may give more information about changes in teacher attitudes and practices. (Contains 8 references.) (SLD)