On the ITBS, Language is about usage (she didn't vs she don't, etc), expression (like where the best place is for a particular sentence to be in a paragraph), writing mechanics (capitalization and punctuation), and spelling.
I've found that the capitalization and punctuation part can be pretty sensitive to whether or not a kid has been explicitly taught those things, the usage and expression is pretty intuitive for a good reader and someone who comes from a home where standard English is spoken, and the spelling is, well, spelling (for us, my natural speller always scored off the charts and it was always my dyslexic son's worst score by about 50 percentile points).
Last edited by Kai; 11/18/12 08:35 AM.