We signed up for both earth and space, and life science. CTY requires 5th grade math, but I'm not sure that's a real course requirement. My guy was 7 and in the midst of third grade math when he tried it. He likes it (and I saw no math so far). If your DS is interested in the subject matter, I expect he'll be fine. I had DS do the demos first - basically, the first lesson, application and test. He enjoyed it and wanted to continue, but he loves science more than any subject.