A person becomes smarter not by nature nor by sudden enlightenment. Essentially, it happens as the brain is continuously used and challenged, gradually forming more and stronger neural connections. The key is to give them "just the right amount of difficulty." If it's too easy, they won't need to think; if it's too hard, they'll give up. Only those challenges that are a bit difficult but solvable with effort will push the brain to establish new connections and optimize pathways.