A Meta-Analysis of Morphological Interventions in English: Effects on Literacy Outcomes for School-Age Children

The purpose of this study is to examine the effects of morphological instruction on language and literacy outcomes by synthesizing 92 standardized mean differences (d) from 30 independent studies. Findings show a moderate overall effect of morphological instruction ([dbar] = 0.32), suggesting that children receiving morphological instruction performed significantly better on measures of literacy achievement than comparison groups. Moderator analyses showed that intervention effect varied depending on the literacy outcome. There were significant and moderate intervention effects on morphological knowledge ([dbar] = 0.44), phonological awareness ([dbar] = 0.48), vocabulary ([dbar] = 0.34), decoding ([dbar] = 0.59), and spelling ([dbar] = 0.30) but not on reading comprehension or fluency. Results also suggested differences in effectiveness related to age and research design but not unit of intervention, scope, length, and learner type. Effect sizes decrease by school level (e.g., greater for younger students than middle school and upper elementary students). Also, there were larger effects for quasi-experimental than experimental studies and for researcher-designed measures than for standardized measures. Implications for educational settings and research agendas are discussed.