My son from about 3.5-almost 4 (which is now) had a whole imaginary class where he was the teacher. I'd always have to leave the car door open long after he was strapped in to allow all his students to get in to. we'd most often take at least some of his students with us where ever we went. He also tended to have gym class with his students while he was in the shower each night. It's only in the last week or two that his imaginary class has disappeared (instead he's been on a learning mission).