Before I read the book to the boys, I had them cut pictures of living things out of old My Big Backyard magazines. I asked them to try and sort them in any way they wanted. Ds#1 had some idea of grouping them as birds, reptiles, mammals, etc. but they had trouble.
Next we sat and read the book up through the part where the professor asks Benny to separate his pictures into those with spines/bones and those without. Next week we'll finish the book having them sort the vertebrates into mammals, birds, fish, reptiles, and amphibians. Maybe we'll put it together as a collage or lapbook.