try the history of economic thought. If your son likes history, he may enjoy learning economics going through its history. I also think Bob is quite charismatic as a teacher. And you may even try to use the history of economics by Rothbard (An Austrian Perspective on the History of Economic Thought) as a textbook, it should be clear enough for a teen.
EDIT: btw I’m not affiliated with liberty classroom, I don’t know why my name is info to be honest, it wasn’t like this in the old forum. Maybe it’s destiny trying to tell Tom to hire me 😀