The current study meta-analyzed single-case design (SCD) and group research regarding incremental rehearsal (IR). We used phi to meta-analyze data from 19 IR studies. Data from the SCD studies resulted in a nonoverlap of all pairs (NAP) score of 98.9% (95% CI = 97.6-100%), which resulted in a weighted phi of 0.77 (95% CI = 0.69-0.83). The group research data resulted in a median "d" of 1.67 (95% CO = 1.43-1.91), which converted to a weighted phi of 0.63 (95% CI = 0.39-0.87). Results suggested that using NAP to compute a weighted phi from SCD research led to a coefficient that was not significantly different from the weighted phi based on group studies z = 46, p less than 0.05, and there was not significant heterogeneity among the effect sizes (Q (k = 17, df = 16) = 11.73, p less than 0.05, I[superscript 2] = 0). Efficiency data resulted in a weighted phi of -0.22 (95% CI = -0.79 to 0.34), which suggested a small effect when comparing the efficiency to other approaches, but the studies used different data to determine efficiency. Suggestions for future research are included.