what we did to train my dog was when we went to take him out, we would put the leash on, bring him to the door, then stop. We would take one of his front paws and make him scratch on the door. After he did that we would go out. After a while, we would bring him to the door, and not let him out until he scratched at the door or we made him scratch. After a few weeks, he got the hint and will go to the door and will scratch at the door or screen until we go get him. If we aren't in the room, he will even scratch at the door to the room we are in until we come out, then he will run to the door and scratch. Just make sure to treat him if he does it on his own. That worked for us, so it should work for you.