This study examined whether inclusion of cognitively guided instruction (CGI) in a mathematics methods course for 34 undergraduate preservice teachers at the University of North Carolina at Greensboro would improve their teaching performance, compared to controls. The Beliefs Survey, with four subscales (Role of the Learner, Relationship between Skills and Understanding, Sequencing of Topics, and Role of the Teacher) was administered four times. The mathematics methods course occurred between the second and third administrations, and student teaching occurred between the third and fourth administrations. The survey revealed that preservice teachers in both cohorts changed beliefs to a more constructivist orientation to teaching mathematics during their professional program of study. In both cohorts, the greatest change in beliefs occurred during the semester in which the mathematics methods course was taught, suggesting that dealing explicitly with mathematics pedagogy influences preservice teachers' thinking about teaching and learning mathematics. The beliefs of the CGI cohort continued to change fairly dramatically during the student teaching semester while the beliefs of the non-CGI cohort did not. In response to open-ended questions, preservice teachers acknowledged the need for teachers to know what children were thinking. There were few suggestions from either cohort on how CGI should be actualized in instruction. Implications for teacher preparation are offered. (Contains 28 references.) (JDD)