I found one of the Horrible Science books last week at a used book store in town. It is the Chaotic Chemistry one. So far he loves it! I think it is written around a 5th-6th grade level so he likes to read it out loud with me but he has really been enjoying it. So far we are only 50 pages or so into it because we keep having to stop for discussions or experiments. We'll definitely be ordering more of these. Thanks for the heads up everyone!