The present study investigated the effect of classroom-based syntactic training on children’s abilities to produce passive sentences. Thirty-three monolingual English children (mean age 5;2), were involved in passive-voice training based on storytelling sessions within a priming design. The training was delivered in a classroom setting, with two classes randomly allocated to either an active sentence or a passive sentence training structure. All children were individually tested at post-training. Children in the passive condition generated 3.6 more passives than the children in the active voice condition. Pre-training language and memory abilities, as measured by both grammatical level with a standardized sentence comprehension task (TROG-2) and a verbal working memory task (Digit Span), were unrelated to number of passives produced at post training. The study supports and expands recent evidence on the benefit of rich language exposure in the classroom context and on the quick dynamic adaptation of the implicit learning mechanisms to language exposure activities.