Kriston-
I have to admit, when I saw that you were asking about unit studies, I sort of did a mental shrug and thought, "That's not us". But you know, we do a tremendous amount of interest led and project based learning. I guess in my mind, "Unit studies" implies a boxed program designed for the average learner, or something Mom or Dad has planned out far in advance with little input from the kids. What you describe though, sounds like what we do much of the time, and how some of our best learning happens.
An example: We read about the British Tudors back when Artemis was four and half. She immediately became fascinated by everything Tudor. At her request, we got many library books on the time period, both fiction and non-fiction. She got into Shakespeare too, on a tangential learning binge. At age five, she designed a Tudor timeline and made illustrations of all Henry's various wives and children. She is eight now and still loves to read about this era. She knows all the wives intimately and can tell you their order and how they were "discharged". She can talk your ear off about Elizabethan fashion, food, etc.
My advice is to work with your son to design your own unit studies, be flexible in how you follow an idea, and don't be afraid to go in unexpected directions.
hth!
