Statistical learning (SL)—sensitivity to statistical regularities in the environment—has been postulated to support language development. While even young infants are capable of using distributional statistics to learn in linguistic and non-linguistic domains, efforts to measure SL at the level of the individual and link it to language proficiency in individual differences designs have been mixed, which has at least in part been attributed to problems with task reliability. In the current study we present the first prospective longitudinal study of the relationship between both non-linguistic SL (measured with visual stimuli) and linguistic SL (measured with auditory stimuli) and language in a group of English-speaking children. One-hundred and twenty-one (N = 121) children in their first two years of formal schooling (Mage = 6;1 years, Range: 5;2 – 7;2) completed tests of visual SL (VSL) and auditory SL (ASL) and several control variables at time 1. Both forms of SL were then measured every 6 months for the next 18 months, and at the final testing session (time 4) their language proficiency was measured using a standardised test. The results showed that the reliability of the SL tasks increased across the course of the study. A series of path analyses showed that both VSL and ASL independently predicted individual differences in language proficiency at time 4. The evidence is consistent with the suggestion that, when measured reliably, an observable relationship between SL and language proficiency exists. Theoretical and methodological issues are discussed.