I am not so sure you can train them to tell you, it's something they do on their own, I think. You just have to watch for his sign. Brodie is 11 months old and when he was about 5 months old he would sit in the middle of the floor and just stare at me and it took me a while to realize that he was telling me he needed to go potty. So now I know as soon as he starts staring at me it's time to go out. If he can see me from the door he will go stand in front of the door like a statue staring, if he can't see me from the door he will sit or stand in front of me and stare until I bring him out.