Science teacher beliefs and classroom practice related to constructivism and factors that may influence classroom practice were examined in this cross-case study. Data from four science teachers in two schools included interviews, demographic questionnaire, Classroom Learning Environment Survey (preferred/perceived), and classroom observations and documents. Using an inductive analytic approach, results suggested that the teachers embraced constructivism, but classroom observations did not confirm implementation of these beliefs for three of the four teachers. The most preferred constructivist components were personal relevance and student negotiation; the most perceived component was critical voice. Shared control was the least preferred, least perceived, and least observed constructivist component. School type, grade, student behavior/ability, curriculum/standardized testing, and parental involvement may influence classroom practice.