I just received this book from my mother, an Academically Gifted Instructor out if our state. We were excited to see how my 5 year old picked up puzzles. He loves the book.

My only concern is with the answer key. For classroom use it assumes there is only one right answer for every child. Page 13, is a perfect example. He was to order pictures of an hour glass from start to finish. He chose all of the sand on the bottom first because "you have to flip it over first". 

In a classroom setting I worry a black and white answer key might bypass an abstract thinkers process.

The exercises are just the right length; short enough that my daughter doesn't get bored and long enough to make it worth the effort! I love that there are clear instructions provided for each activity at the beginning of the book. This has been a gentle but thorough introduction to critical thinking problems for my four year old.