Powerful learning environments (PLEs) are based on a social constructivist theory of learning, providing a stimulating, resource-rich and inquiry-supportive environment for student self-regulated learning. Fidelity of implementation (FOI) for such PLEs is dependent on several factors, the most critical factor being the teacher's belief system, philosophy of education, and dominant teaching style. This paper examines a classroom intervention implemented in Ontario, Canada grade 10 mathematics classrooms, using theoretical frameworks to first qualify the intervention as a PLE and then evaluate FOI, identifying the critical factors on which fidelity of implementation depend.