The present review examines research on the effects of educational technology applications on mathematics achievement in K-12 classrooms. Unlike previous reviews, this review applies consistent inclusion standards to focus on studies that met high methodological standards. In addition, methodological and substantive features of the studies are investigated to examine the relationship between educational technology applications and study features. A total of 74 qualified studies were included in our final analysis with a total sample size of 56,886 K-12 students: 45 elementary studies (N = 31,555) and 29 secondary studies (N = 25,331). Consistent with the more recent reviews, the findings suggest that educational technology applications generally produced a positive, though modest, effect (ES = +0.15) in comparison to traditional methods. However, the effects may vary by educational technology type. Among the three types of educational technology applications, supplemental CAI had the largest effect with an effect size of +0.18. The other two interventions, computer-management learning and comprehensive programs, had a much smaller effect size, +0.08 and +0.07, respectively. Differential impacts by various study and methodological features are also discussed. (Contains 15 tables.)