Parent coaching from 6 to 18 months improves child language outcomes through 30 months of age.

Interventions focused on the home language environment have been shown to improve a number of child language outcomes in the first years of life. However, data on the longer-term effects of the intervention are still somewhat limited. The current study examines child vocabulary and complex speech outcomes (N = 59) during the year following completion of a parent-coaching intervention, which was previously found to increase the quantity of parent-child conversational turns and to improve child language outcomes through 18 months of age. Measures of parental language input, child speech output, and parent-child conversational turn-taking were manually coded from naturalistic home recordings (Language Environment Analysis System, LENA) at regular 4-month intervals when children were 6- to 24-months old. Child language skills were assessed using the MacArthur-Bates Communicative Development Inventory (CDI) at four time-points following the final intervention session (at 18, 24, 27, and 30 months). Vocabulary size and growth from 18 to 30 months was greater in the intervention group, even after accounting for differences in child language ability during the intervention period. The intervention group also scored higher on measures of speech length and grammatical complexity, and these effects were mediated by 18-month vocabulary. Intervention was associated with increased parent-child conversational turn-taking in home recordings at 14 months, and mediation analysis suggested that 14-month conversational turn-taking accounted for intervention-related differences in subsequent vocabulary. Together, the results suggest enduring, positive effects of parental language intervention and underscore the importance of interactive, conversational language experience during the first 2 years of life. RESEARCH HIGHLIGHTS: Parent coaching was provided as part of a home language intervention when children were 6-18 months of age. Naturalistic home language recordings showed increased parent-child conversational turn-taking in the intervention group at 14 months of age. Measures of productive vocabulary and complex speech indicated more advanced expressive language skills in the intervention group through 30 months of age, a full year after the final intervention session. Conversational turn-taking at 14 months predicted subsequent child vocabulary and accounted for differences in vocabulary size across the intervention and control groups.