Background: Young children clearly know quite a bit about the conventions of written language; for instance, 5-year-old children are sensitive to the fact that words tend to include both consonants and vowels, rather than just one or the other. The core theoretical debate lies in whether this understanding of sub-lexical orthographic regularities predicts children's reading development. To provide empirical data on this question, we examined whether individual differences in sub-lexical orthographic knowledge were related to gains in word reading over a year. Methods: We measured sub-lexical orthographic knowledge in Grade 1 by asking children to choose which of two letter-strings looked most word-like--one containing vowels and consonants and one containing all consonants or all vowels (e.g., "vack" vs "vgck" or "uaie," respectively). Children completed control measures of phonological awareness, vocabulary and nonverbal ability in Grade 1. Word reading was measured in both Grades 1 and 2. Results: Linear regression analyses identified a small but significant and unique contribution of sub-lexical orthographic knowledge in Grade 1 to word reading in Grade 2, after controls for the above measures as well as age, parental education and the auto-regressor of Grade 1 word reading. Conclusions: This finding suggests a role for knowledge of sub-lexical orthographic regularities in children's gains in word reading.