As homeschooling mothers ourselves, we know how limited time and energy are. CGC was designed for multi-level teaching. The lessons are set up to use once a week for a 1 1/2 to 2 hour block of time. It can easily be extended to use over a 2-3 year time period, and it would be helpful to go through it again with the younger children when they reach 5-6th grade level. You might even have the oldest child teach it to the younger ones and get teaching skills while she/he is reviewing basic science!