This primer on two groups of reptiles is a good one to use with primary students who are learning to classify. The text is clear and precise, with supporting elements like a glossary and diagrams to help readers along. Large, double-page illustrations make the book appropriate for reading aloud or sharing at a center. I found a few of the vocabulary words a bit unscientific—probably a concession to reading level. For instance, the definition of the difference between sand and dirt would be debated by an Earth scientist. Some of the details would need much more explanation as well; the difference between oxygen and air, the concept of "taking oxygen out of water," and use of the technical term hibernation for a poikilothermic (cold-blooded) animal, would all prompt questions from young listeners that the book doesn't answer. But overall this is an attractive and useful book. If a teacher takes just a bit of extra time to brush up on the more complete answers to students' inevitable questions, it will be both interesting and developmentally appropriate. The skills that the book reinforces help students go beyond just reading about facts. The basic premise of the "What's the Difference" series would support lessons in classification in all elementary grades. http://www.nsta.org/recommends/ViewProduct.aspx?ProductID=20366