This observational study examined the Iranian mothers' interaction with their typically developing children aged 13-18 months during free play at home (n = 40). The first aim was to determine the main type of Iranian maternal verbal responsiveness. Another aim was to investigate the impact of concurrent prediction of maternal verbal responsiveness and children's communication acts on children's vocabulary. The results showed that the frequency of follow-in directive responsiveness was significantly higher than those of the other two types of responses. Among the various types of probabilistic variables predicting the status of children's vocabulary, the follow-in directive responses of the mothers and the level of communicative acts of children had a significant predictive role in children's vocabulary status. These results suggest that in non-western cultures, a directive interactional style that follows the child attentional focus and the child's own communication acts have a transactional influence on the child language status.