My geometry class, ages 8-11, loved the book...for two primary reasons, I think. First, they loved the taunting exchanges between the hamsters and the cat. Second, after having talked about angles in class, they understood some basics and could apply their knowledge to another "real" situation.
*Hmmm. I can't find notes about this on my blog. Hate it when I forget to write something from a lesson. I had the kids hold up two popsicle sticks and make acute, obtuse, straight, and right angles. We also looked at the vocabulary in Sir Cumference and the Great Knight of Angleland... the "'cute" steeply angled rooftops (acute angles) and the Mountains of Obtuse (obtuse angles
Workbox activity: after learning about acute, obtuse, straight, and right angles, have children form them with popsicle sticks and draw models in their math journals. Read the two books mentioned here.