According to a study published in the December 2008 Journal of Speech, Language, and Hearing Research, children in second grade with language impairments have a pronounced delay in word recognition and reading comprehension that remains delayed through tenth grade. This delay, however, only widens slightly for reading comprehension, and does not widen at all for word recognition.
The study, by Hugh Catts, Mindy Sittner Bridges, Todd Little, and J. Bruce Tomblin, compared the development of over 600 kids with language impairment and normal language over a nine grade span. The authors stressed that while the delays did not worsen or worsen much over this time, they did not get smaller either. This lends strength to the assumption that early language impairment is an excellent indicater of later reading disability.
Implications? More screening early on, and also more in-depth screening. In addition to looking at phonological awareness and letter knowledge, early screening would be most effective if it also looked at vocabulary, grammar, and narration abilities.