This study examined the impact of teacher professional development aimed at improving the capacity of primary teachers in disadvantaged schools to strengthen children's expressive and receptive oral language skills and early literacy success in the first 2 years of school. Fourteen low-SES schools in Victoria, Australia were randomly allocated to a research (n = 8) or control arm (n = 6), resulting in an initial sample of 1254 students, (n = 602 in research arm and n = 652 in control arm). The intervention comprised 6 days of teacher and principal professional development (delivered by language and literacy experts), school-based continuing contact with the research team and completion by one staff member of each research school of a postgraduate unit on early language and literacy. Schools in the control arm received standard teaching according to state auspiced curriculum guidelines. Full data were available on 979 students at follow-up (time 2). Students in the research arm performed significantly better on Test of Language Development: Primary (Fourth Edition) sub-tests (p ≤ .002) and the Reading Progress Test (F = 10.4(1); p = .001) than students in the control arm at time 2. Narrative scores were not significantly different at time 2, although students in research schools showed greater gains. Findings provide "proof of concept" for this approach, and are discussed with respect to implications for teacher professional development and pre-service education concerning the psycholinguistic competencies that underpin the transition to literacy.