This study examined interventions for addition and subtraction that were implemented through single-case design (SCD) research studies. We attempted to extend prior SCD meta-analyses by examining differences in effect sizes across several moderating variables and by including a novel index of effect, improvement rate difference (IRD). We also examined the extent to which effect sizes differed by degree of experimental control achieved in the studies. Forty-seven effect sizes were obtained across 11 studies. IRD effect sizes ranged from 0.59 to 0.90 and suggested a moderate to large effect for the math interventions. Variables that appeared to moderate the effects were student age, time spent in intervention, and intervention type. We also identified a relationship between experimental control and the obtained effect sizes. Findings indicated that further SCD research in basic arithmetic and rigorous experiments are necessary to establish an evidence base that accurately characterizes intervention effectiveness.