http://www.lexile.com/about-lexile/grade-equivalent/grade-equivalent-chart/They do acknowledge the whole Can Read != Should Read thing here as well:
Although a student may be an excellent reader, it is incorrect to assume that he or she will comprehend text typically found at (and intended for) a higher grade level. A high Lexile measure for a student in one grade indicates that the student can read grade-level-appropriate materials at a very high comprehension rate. The student may not have the background knowledge or maturity to understand material written for an older audience. It is always necessary to preview materials prior to selecting them for a student.
We've always had to discount the novelty of DS's "reading level" test results, but instead use his "actual" reading levels as a progress chart to keep him moving forward.
