Improvement in oral language interventions: Differences and relation between effects on treatment-inherent measures and effects on standardized tests

Whether the effects of an oral-language intervention is tested with measures of trained vocabulary (treatment-inherent tests) or standardized measures (treatment-independent tests) can have consequences for the mean effect size in meta-analyses. Moreover, based on a theory of transfer effects, effects on the trained words could serve as an index of how much benefit is gained by children from the intervention. We present a meta-analysis that assesses the differences and relation between the intervention effects of these two types of outcomes, trained vocabulary and standardized vocabulary tests. The results show large effects on trained vocabulary, limited effects on standardized measures, and no clear relation between the two. The moderator analysis indicates that less instruction time is associated with larger effect sizes on trained vocabulary but that trained vocabulary is not a predictor of either standardized expressive or receptive vocabulary. Thus, in interventions and meta-analyses, it is important to distinguish between effects on trained vocabulary and standardizedtests, and trained vocabulary effects does not necessarily transfer to standardized measures. This indicates that effects on trained vocabulary outcomes provide limited information when evaluating language interventions.