Darwin and his class visit the La Brea Tar Pit and the nearby museum to learn about dinosaurs. In alternating chapters, Darwin slips from the museum tour into a world in his own imagination. During the tour, Miss Tell, their teacher, tells them about the dinosaurs - when they lived, what they ate, how much they weighed and some information about how they died. Darwin daydreams about saving each of them from the death Miss Tell tells them about.
The book doesn't specifically say, but I think this book is most appropriate to the 9 to 12 age group. There are few illustrations, just small black and white drawings at the top of each chapter; they add nothing to the story. The story itself is all right, nothing spectacular and not terribly well-written; the best thing it has going for it is the information it provides. The alternating chapters doesn't really work particularly well, but kids might enjoy the kid-as-hero aspect.
For the parents who worry about messages, Darwin tells several lies - to a pack of dire wolves and a saber-tooth - and, when his classmate, Amy, complains that no one ever believes HER fibs, he suggests that she should practice more. Since the book is overall really average, it might not be worthwhile to get it, only to send your child the "practice makes perfect, even when it comes to lying" message.