Disentangling the far transfer of language comprehension gains using latent mediation models

While we know that interventions targeting oral language can be effective, little is known about what drives these effects. In this study, we examine whether gains in transfer measures are mediated through the specific words that are trained in a language intervention. Based on a large-scale randomized controlled trial of language intervention in 4- to 5-year-old children, latent mediation models were used to disentangle oral language gains in transfer measures. The results first showed that the effects of the language intervention and the transfer effects are generated through expressive rather than receptive measures of language. Second, we found that the effects of the intervention on intermediate transfer measures of language were mediated through the ability to define the trained words. Third, and critically, for far transfer measures that did not contain any of the trained words, the effects were mediated through the trained words. The findings relate to theories of transfer and support the idea that far transfer is possible, at least within the same domain. In addition, it seems that effects on receptive language skills are difficult to obtain and that what is improved is instead the children's ability to express themselves and use procedures to explain words. Thus, to optimize intervention effects, future studies should focus on expressive language.