Textbooks.
Besides classroom style learning has prooven(ha ha, yeah I know, taboo word) to be a less effective learning system than textbooks and/or personal teacher/tutor.
Think of it this way, anyone can teach someone to read. It's not hard at all, just takes some time. Once a child can read, he can pretty much learn anything. He's not limited by the teacher, he's limited by his textbooks. Homeschooling is not the parent trying to tell their kid everything academic they know. The parent really just directs the learning. AKA making sure they're doing it.