The purpose of this mixed method research study was to examine the constructivist beliefs and instructional practices of secondary science teachers. The research also explored situations that impacted whether or not student centered instruction occurred. The study revealed science teachers held constructive beliefs pertaining to student questioning of the learning process and student autonomy in interacting with other learners. Teachers held the least constructivist beliefs pertaining to student teacher collaboration on lesson design. Additionally, teacher beliefs and practice were not congruent due to instructional practices being deemed less constructivist than reported. The study found that curricular demands, teacher perceptions about students, inadequate laboratory resources, and the lack of teacher understanding about the components of constructivist instruction inhibited student centered instruction. The results of this study led to six recommendations that can be implemented by school districts in collaboration with science teachers to promote constructivist instruction.