This article reports on a comprehensive literature review and meta-analysis of 68 experiments on teaching mathematics to individuals with significant cognitive disabilities. Most of the studies in the review addressed numbers and computation or measurement. Within the computation studies identified, most focused on counting, calculation, or number matching. For the measurement studies, nearly all focused on money skills. Of the 54 single subject design studies, 19 were classified as having all quality indicators for research design (13 representing the National Council of Teachers of Mathematics Measurement standard and 6 representing the Numbers and Operations standard). These studies offer strong evidence for using systematic instruction to teach mathematics skills and for using in vivo settings. (Contains 1 figure and 7 tables.)