AntsyPants: not a solution, because I think they have to read within 150 points of their level (-100, +50).

Here is the funny thing. Our school uses DRA rather than Lexile, and they don't test (or rather they last tested in May, at which point my DS7 was supposedly below a lexile 200 in English). The last book he read independently at home was a lexile 700. He doesn't test well, but I also noticed something of a trend in his Accelerated Reader reports: if the book is way below his level he tends to score worse. The more challenging the book (and I picked that 700L book -- shorter, written bigger than the 590L books he currently reads with his father -- as an easier independent read, which shows how... unintuitive leveling is) the better he does on the quizzes. Weird?