Teacher behavior associated with effective mathematics instruction in elementary schools had earlier been characterized and translated into an instructional program. Key instructional behaviors identified were: daily review, development, seatwork, homework assignment, and special reviews. A vigorous test of this program was undertaken using 40 fourth-grade classroom teachers. Teacher effectiveness was measured by student gains on scores on a standardized achievement test. The performance of the treatment group significantly exceeded the performance of the control group. A complete analysis is reported. (MP)