Unpacking language richness as a predictor of bilingual children’s language proficiency

The richness of bilingual children’s language experience is typically expressed as a composite score using parental questionnaire data. This study unpacks the concept of input richness by examining one such composite score (Q-BEx; De Cat et al., 2022b) to determine whether it reliably predicts children’s language abilities, is no more complex than required, and as user-friendly as possible. Data were collected from 173 bilingual children aged 5 to 8 across three countries (France, Netherlands, UK) with various heritage languages in each. Parents completed the Q-BEx questionnaire and children proficiency tasks in their societal language. We analysed the predictive power of the original score compared to several alternatives. Results showed (i) these alternatives were not more informative, (ii) scores including qualitative aspects of richness fared better than those with only quantitative variables, (iii) the latent variables underlying richness were comparable across languages, and (iv) whether SES was included made little difference.