In this article, we narrow our investigation to the talk provided by one teacher in the exploration phase of a primary school science project. The exploration phase warrants attention given its role in providing students with a common base of science activities that draws on their prior knowledge. We examine lesson excerpts from a grant-winning primary years science teacher who sets up her Year 3 students to explore garden ecosystems. The study's analytic framework is derived from Systemic Functional Linguistics and focuses on the way the teacher uses certain aspects of ideational, interpersonal and textual functions to mediate between the instructional and regulative discourses. Our findings show that the teacher orientated to the regulative discourse to provide students with access to an instructional discourse. Additionally, the teacher used a significant number of pronouns for signalling, and sequencing connectives that flowed on to a significant number of complex noun groups. We draw attention to the range of speech functions and comment on their role in school science lessons.