This book is a wonderful collection of unit studies for small children. I am using it with my 2 yr old and 4 yr old. It is perfect for the 2 yr old but not challenging enough for the 4yr old. However, we do sincerely enjoy the books and discussing them together. I will start Five In A Row with the 4 yr old soon and I will use Before Five In a Row with my 2 yr old, and someday, our 3rd child. I do think that including so many out of print books (5+ out of 22) is a terrible disadvantage. At the very least, alternative books should be included with these units. In my opinion, this reduces the value of the book. I wish I had not paid so much.