This study examined changes in 19 teachers' beliefs across the first 2 years of a professional development program in cognitively guided instruction (CGI). The study involved five teams of mathematics teachers and teacher educators. Teams attended professional development workshops on several occasions. Each team met monthly to discuss their progress. The teachers received a visit each month during mathematics instruction from one of the teacher educators and once each semester from a researcher and an experienced CGI teacher. Data collection occurred during the first day of the three day workshops. Participants responded to three sets of open-ended questions that examined what they believed teachers needed to know to teach mathematics effectively, what they considered the important outcomes of primary mathematics instruction, and what they considered the most important aspects of teaching primary mathematics. Participants changed their beliefs in three areas (teacher's view of children, teacher and student roles, and skill acquisition and problem solving) over the 2 years, with changes varying by category and grade level. Eight teachers continued to refer to children's needs collectively. Four teachers continued to believe that their major role was to impart knowledge to children rather than provide experiences whereby children can construct their own knowledge. Two teachers believed that skill acquisition was the most essential outcome of mathematics instruction. (SM)