Because we included studies from a

Because we included studies from a wide age span and on different mathemat- ics and cognitive skills, we hypothesized that the research body is reporting a distribution of effect sizes with significant between-studies variance, as opposed to a group of studies attempting to estimate one true effect size. Thus, we used a random-effect model for the current study (Lipsey & Wilson, 2001). Weighted, random-effects meta-regression models using Hedges et al.’s (2010) corrections were conducted with ROBUMETA in Stata (Hedberg, 2011) to summarize effect sizes and to examine potential moderators.