I agree it's a rough tool and can't capture many of the nuances of reading. It doesn't provide much useful information about what I call "reading endurance." I consider DD7 a marathon reader and have to pry books out of her hands so she gets enough sleep. DD5 has a high reading level with good fluency and comprehension but is working on building her up her endurance.
Lexiles have been useful tools in busting DDs out of the grade-level reading boxes at school. It's an on-going reminder all first graders shouldn't be reading books aimed at first graders. I just wish there was a similar tool to help bust out of the grade level math boxes too!
