The purpose of this investigation was to identify the changes in (n=8) inservice teachers' conceptions or knowledge structures of mathematics and subject specific pedagogy as the teachers participated in a two-year pilot professional development program and began teaching middle school mathematics. Data collection consisted of a questionnaire, interviews, and a unit work sample. Teachers in the study had not previously taught secondary mathematics. Results showed that teachers' own experiences in learning mathematics indicated these inservice teachers had been taught mathematics in the early grades by worksheets, drill and practice, memorization, and flash cards. Although participants reported feeling more confident and able to present mathematics to students using a variety of approaches, several statements and videotapes of their teaching presented conflicting views. The conceptions/knowledge structures of the teachers regarding mathematics teaching did not change significantly. (MKR)