Malcolm Lewis:
Excellent workbooks to help your kids catch up or get ahead at school. Each book contains a whole year of curriculum-based exercises and activities. Approx 300 pages per book.
I got one each for our kids to complete over the summer so they get off to a strong start when school starts in the Fall. Depends on how much time they spend on the per day, but figure around 4-8 weeks with 20 mins/day.