In this original research, the effect of a single 40 minutes parent-implemented language intervention on modification of parent/child communication features is tested. Furthermore, this study attempts to answer a current controversy in the literature wherein the relationship between adult language input and child language development are explained by two hypotheses: the structural hypothesis (critical role given to an adult’s input characterized as short, simple and redundant) and the pragmatic responsivity hypothesis (importance of contingency between child’s utterances and the adult’s responses. Furthermore, in order to answer these questions, this study explores the respective impact of a formal (structural hypothesis) or pragmatic (responsivity hypothesis) modification of parental language input on preschoolers’ communication skills and behavioral characteristics. Sixty 4 year-old typically developing children and their parents will be recruited from normal schools in several regions in the French-speaking part of Belgium. Parent-child dyads will come to the laboratory and participants will be randomly allocated to structural group (formal modifications of parental language), pragmatic group (enhancement of contingency between child’s utterances and adult’s responses) or control group (no manipulation of parental language input). All tasks will be video-recorded and all language samples in free play transcribed with CHILDES enabling the measurement of parent’s and child’s Mean length of utterance (MLU) and Mean Length of Turn taking (MLT). The results reveal that after this short pragmatic intervention, children increase and parent decrease their MLT. So turn taking ratio become more equilibrate. Furthermore, after the structural intervention, children increase their MLU but no modification of parent’s MLU is observed. As this study aims to explore the relation between language and externalized behaviour in preschooler’s further analyses will be realized with Crowell procedure, a grid who analyse child behaviour and affects during interaction with the parent.