Single-case design (SCD) is a quantitative experimental technique in which participants serve as their own control. The use of an effect size in SCD allows evaluation of outcomes as well as comparison of outcomes via meta-analyses. Characteristics of SCD research make the selection of an appropriate effect size complicated. Additionally, there are a number of factors that complicate the use of SCDs as a means to improve academic skills. The purpose of this study was to examine patterns by which SCD effect sizes are used to quantify outcomes from academic interventions. To do so, a descriptive analysis of an extant database of SCD studies was conducted. The authors created frequency tables for each effect size identified in the database as well as graphs to show the extent to which the use of effect sizes changed over time. The authors also determined whether the most frequently used effect sizes were appropriate for summarizing changes in academic outcomes. Although many effect sizes have been developed, only a small number are routinely used in SCD research for academic skills. The most frequently used effect sizes were those that come from standardized statistics, compared with those that utilized principles of regression or Bayesian analysis.