This review summarizes research on the effects of technology use on mathematics achievement in K-12 classrooms. The main research questions included: (1) Do education technology applications improve mathematics achievement in K-12 classrooms as compared to traditional teaching methods without education technology?; and (2) What study and research features moderate the effects of education technology applications on students' mathematics achievement? Over 700 potential studies were identified for preliminary review in an extensive search of previous studies, which included a comprehensive literature search of articles written between 1970 and 2011. Producers and developers of educational technology programs were also contacted to check whether they knew of any studies that had been missed. After applying consistent inclusion standards, a total of 74 studies met the inclusion criteria and were included in the final review. These had a total sample size of 56,886 K-12 students. The three major categories of education technology reviewed were: (1) Computer-managed learning; (2) Comprehensive models; and (3) Supplemental computer-assisted instruction (CAI) technology. The overall effect size weighted by sample size was +0.16, a modest effect. Outcomes were broken down by type of intervention, grade level, program intensity, and socio-economic status. Findings of this review suggest that educational technology applications produce a positive but small effect (ES=+0.16) on mathematics achievement. Supplemental CAI technology had the largest effect, with an effect size of +0.19. The other two categories, computer-managed learning and comprehensive models, had much smaller effect sizes, +0.09 and +0.06, respectively. Educational technology is making a modest difference in mathematics learning. The evidence to date, however, does not support complacency. New and better tools are needed to harness the power of technology to enhance mathematics achievement for all children. [For the full report, "The Effectiveness of Educational Technology Applications for Enhancing Mathematics Achievement in K-12 Classrooms: A Meta-Analysis. Best Evidence Encyclopedia (BEE)," see ED527573.]