Acculturation has consequences for immigrant health, and provides a natural experimental context in which to test Fonagy and Allison’s theory of epistemic trust. Their theory posits that secure attachment in the caregiver-youth dyad is a key mechanism for supporting, and exposure to childhood adversity and trauma is thought to block, the cultural learning process. The aim of this study was to validate the theory of epistemic trust by examining secure attachment as a predictor of acculturation across time and adverse childhood experiences as a moderator in 100 recently immigrated high school students followed for one year. Growth parameters were extracted and regressed on key study variables. Results indicated a significant main effect of maternal attachment on acculturation across time, as well an interaction in which the aforementioned link was blocked by adverse childhood experiences. In the context of acculturative learning, two tenets of the theory of epistemic trust were supported.