We are somewhat dealing with this issue - where DS6's reading level is quite high, but as his teacher said, the materials at his level are either not appropriate or interesting to him... and he is the only one in his class that high, so they have pulled him to one-on-one instead of placing him in a reading group that would bore him.
Since the gap between his writing and reading is quite large (writing is basically age-level), they are using this time to work on writing (for instance, using the book that he is reading in class as prompts for writing exercises). In cases where you have a child that is so wildly asynchronous - working on the areas where the gaps are significant between skills is probably a better focus than strict Lexile numbers. This is what DS's teacher is doing... so although they are working reading wise at his level, they are shifting focus to encourage more growth in the weaker areas.
In his own free time, he reads through the large book collection in the classroom (we are very fortunate that they have books for all levels up to chapter books even though his room are all 5-6 year olds) which he loves - in fact, the big problem we are facing is that he tends to ignore the world (including teachers, sigh) when he gets into a book (and it is like that at home which drives me batty - especially when he is naked, shivering - sitting next to jammies and reading because the book caught his eye instead of putting on his jammies).
