I am using this with my 1st grade son. The lessons are short and concise. The variety and number of problems in each lesson are enough to keep his attention. We often do 2 lessons without losing his attention.
I like how the concepts are repeated throughout the book. I do feel (at least for my son who catches on quickly) that this level is not challenging enough for him. Could this level be below suggested level? To compensate, I often do 2 lessons a day with him.