In this meta-analytic study, we investigated the effects of mobile devices on student achievement in science, mathematics and reading in grades K-12. Based on our inclusion criteria, we searched the ERIC and PsycINFO databases and identified 14 peer-reviewed research articles published between 2010 and 2014. We identified the device type, subject area, intervention language, grade level, study design and implementer (i.e., of the intervention) as potential moderator variables that may influence student achievement in the targeted content areas. We followed a three-level meta-analytic procedure to estimate the overall effect of these variables and explain the variation in outcomes. The results suggest that use of mobile devices in teaching yielded higher achievement scores than traditional teaching in all subject areas. With regard to the analysis of moderator variables, the results suggest that using mobile devices in reading is significantly more effective than doing so in mathematics.