Abstract: | Home‐visiting programs have gained increasing importance in family‐centered prevention and intervention. However, few studies have examined the mechanisms underlying early intervention treatment effects. The goal of this study is to analyze the mediating role of maternal sensitivity in enhancing language development with the home‐visiting program Parents as Teachers (PAT). Data were collected and analyzed within the ongoing, long‐term ZEPPELIN study, a randomized controlled trial with 251 participating at‐risk families. Via longitudinal mediation analysis, we examined whether effects of the PAT on receptive and expressive language outcomes at 24 and 36 months were mediated by maternal sensitivity at 12 months. Within a moderated mediation framework, we investigated whether the level of family psychosocial stress affects this mediation. Results showed that intervention effects on language outcomes are mediated by maternal sensitivity—weakly and through specific pathways. Moderation and moderated mediation analyses indicated that effects of the PAT and also specific mediation effects increase with the level of psychosocial stress. Implications of the results for practice are discussed. |