“…Two separate studies (Craig, Thompson, Washington, & Potter, 2004;Craig, Zhang, Hensel, & Quinn, 2009) used a subsample of a larger study , but investigated different outcomes, and these three were combined to form one study. Another three studies provided outcomes disaggregated by grade level (Charity, Scarborough, & Griffin, 2004, Grades K-2; Kohler et al, 2007, Grades 1 and 3; Terry, 2006, Grades 1-3), resulting in a total of 20 observed study effect sizes. From these studies, 75 outcome effect sizes were coded: 59 for reading and 16 for writing and spelling; a simple mean was computed for the study's overall effect size.…”