Even treating it as a purely optional reward didn't work, at least for me. I remember doing AR and treating it like a game -- find the most points-dense book possible in the school library (for me it was The Hobbit, a whopping 70 points), read a summary of it online to get the details and ace the test. All without even opening the book. Well, I actually did try reading The Hobbit but I couldn't make it past the handful of pages without falling asleep.