Dull classroom environments, poor students' attitudes and inhibited conceptual development led to the creation of an innovative mathematics program, the Class Banking System (CBS), which enables teachers to use constructivist ideas and approaches. To assess the effectiveness of the CBS, the Individualised Classroom Environment Questionnaire (ICEQ), Constructivist Learning Environment Survey (CLES), Test of Mathematics-Related Attitudes (TOMRA), and concept map tests were administered to two groups of fifth-grade students as pretests and posttests over an academic year. To enrich the data collected from those questionnaires, three case studies (one for the experimental group and two for the control group) were undertaken based on observations and interviews of selected students. Relative to non-CBS students, CBS students experienced more favorable changes in terms of mathematics concept development, attitudes to mathematics, and perceived classroom environments on several dimensions of the CLES (e.g., Personal Relevance, Shared Control) and the ICEQ (e.g., Participation and Differentiation). Qualitative information based on classroom observations and student interviews reinforced and enriched the patterns of results obtained from the concept test and questionnaires.