I was talking to a 2nd grade teacher who had a student reading on level W. She pointed out that even if a kid can comprehend texts 3 grade levels ahead of her, she still could benefit from developing more comprehension skills using easier texts.
Remember that the reading level tests are just asking kids to read a short passage and ask some quick questions and that extrapolates they can read whole books at that level. But they still need more instruction in comprehension strategies.