The effects of morphology instruction on literacy outcomes for children in English-speaking countries: a systematic review and meta-analysis

In this pre-registered meta-analysis, we investigated the effectiveness of morphology instruction on literacy outcomes for primary school children in English-speaking countries. We were interested in overall reading and spelling outcomes, but we also looked separately at results for trained and untrained words in order to determine whether there was evidence of transfer to untrained words. We were also interested in whether results transferred beyond the word level to reading comprehension outcomes. Our screening process revealed 28 eligible studies, which contributed 177 effect sizes to the analyses. Robust variance estimation methods were used to account for dependence between effect sizes. Overall, effect sizes on reading and spelling outcomes were small to moderate. Effect sizes were larger for trained words than untrained words. There was evidence of transfer to untrained words for spelling outcomes, but not for reading outcomes. There was also no clear evidence of effects on reading comprehension outcomes. In general, the evidence was characterised by large amounts of heterogeneity and imprecision, which was reflective of the wide variety within and between studies in terms of intervention content, outcome measures, intervention dosage and type of control group. We discuss the limitations of the current literature and make recommendations for future research and practice in the field of morphology instruction.