My son was asked to do a project on a type of weather and he selected Tornadoes. I purchased this book for him to read for his fact finding. My son is in 2nd grade. We went through the book several times and I will say that it is very well done. It is highly informative about tornadoes, chock-full of facts, and the pictures do a good job of representing a tornado. I actually learned quite a bit myself that I was not aware of.
HOWEVER, I strongly disagree with giving this book an age classification of 6 and up as it is classified on Amazon. I would venture to say that most kids in this age range are not mature enough to handle the full details about tornadoes presented throughout this book. My son is very mature for his age and just a few weeks shy of being 8. Yet this book was just way too much for him. He actually got very teary at the end of the book and started asking me all kind of questions. Yes, I'm glad he learned a lot from the book, but I would say this is more appropriate reading material for an older child. The book is vey explanatory and even talks about how may people died in one of the worst tonadoes in history. In addition, as we happen to live in Florida and one of the states called out as having a large number of tornadoes this became a huge fear factor for him. I don't feel that the end of the story made him feel more assured in it's closure that he would be safe.
So, in a nut shell, you know your child best. This book is very well done for a child with the right age and maturity. For me, I wish I hadn't made the purchase and waited until he was a bit older. I'd venture to say like 4th or 5th grade. Keep in mind that my child normally has no problems with things that are fairly intense (like star wars movies and such) yet this book totally frightened him. Probably because it's a little too real to life.