One Fish, Two Fish, Red Fish, Blue Fish is a classic in the Dr. Seuss world. This book is great for all ages because it highlights creativity and, like many of Seuss' books, shows that a little nonsense can be a good thing. This book can be used with many different units It focuses on opposites, counting, colors, descriptive language... there are so many different opportunities. Of course, I would use this in a Dr. Seuss unit. I would use this book for grades K - 2. The Guided Reading level is K and the Lexile level is 180L.