After you complete the blue flame challenge Flitwick will give you forty points, after you talk to Ron, I saved the game and came back to it later and I got another forty point. I found out that after you talk to Ron, save it and then quit, come back to the game and Flitwick will keep giving you forty points.
This cheat is very simple. You can only do this on the level that you act as Goyle. So when you are acting as Goyle let a prefect see you. When your caught Slytherin will lose 5 House points. You can do this as many times as you want.