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, actual and preferred versions of the Individualized Classroom Environment Questionnaire (ICEQ), the actual version of the Constructivist Learning Environment Survey (CLES), the Test of Mathematics-Related Attitudes (TOMRA), and conceptual map tests were administered to two groups of 5th-grade students as pre-tests and post-tests during the course of 2 academic years. To enrich the data collected from these questionnaires, three case studies were undertaken based on observations and interviews of selected students. A comparison of Class Banking System (CBS) students with non-CBS students suggested that CBS students experienced more favorable changes in terms of a mathematics concept test, attitudes to mathematics, and perceived classroom environments on several dimensions of the Constructivist Learning Environment Survey (e.g. Personal Relevance, Shared Control) and the Individualized Classroom Environment Questionnaire (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 in that it supported the effectiveness of the CBS in providing elementary mathematics students with a constructivist and individualized classroom learning environment that promotes both conceptual development and positive attitudes. (Contains 48 references, 7 figures, and 4 tables.) (Author/MM)