I think you are on to something. At the same time I wonder about content sticking if you don't practice the subject for months. Doing math two months of the year (ignoring the math you might need in physics class) might mean you have to rehash a lot. That said, for many subjects this wouldn't even change anything. How often does learning something in history class currently rely on what you learned a few months ago? Rebec in my biology classes things rarely were connected. For a few weeks we talk about fungi and then for a few weeks about the cardiovascular system.