I love AR. I used it in my classrooms and the kids absolutely loved it; they set individual goals for points, stored in their desks. It helps them have some independent texts on top of what I assign that they can actually read, so that they can sit at their desks and quit bugging me, and actually enjoy what they're reading (It's important to have a very wide variety of texts) Without levels, students tend to choose things that are too hard, and therefore aren't effectively reading, and AR is way more interesting than Basal readers, which is the other dry, horrible option for a struggling child. It also makes creating reading groups a breeze when combined with direct testing. My rule was three texts per child: one from me, one AR, and one free choice of any level (untested) in their desk at all times. Positive implementation is key, but my classes adored AR.

Mina's school uses lexile, which does help me pick some independent texts for her as gifts, but she has access to texts up to high school level, should she choose.