This paper discusses a study that considered how the quality of three different learning environments, indoor classrooms, outdoor classrooms and forest schools, for children aged 3-5 years, is associated with the quality of their utterances. Adopting a theoretical framework of interactionism it was found that, within the study settings (n = 4), the quality of utterances differed depending on the environment in which the children were playing and learning. The data were collected through a phased approach, firstly by undertaking interviews, with children, parents, practitioners and experts, (n = 63). These interviewee responses defined the features of a high-quality environment to promote speech and language. The second phase, using the features identified, resulted in an audit tool which was used to assess different environments. By then analysing lexical diversity, through observations (n = 43) using body-worn cameras attached to children using chest harnesses, alongside the environmental audit, a positive association was found between the quality of the environment and the quality of children's utterances. It is asserted therefore that it is possible to define a high-quality environment, for the purposes of language development.