well, sir, i get what you are trying to do. sadly, this is impossible, or you could just uninstall the game until your child get's responsible again. My dad tried this too, because like a year ago i played too much of those games too. He didn't find anything that would help, so he just uninstalled all the games. Now i am more responsible for myself and get good grades

I have always gotten good grades, but my father was bothered because i sat too much in front of a screen all day. But i did my homework :p So just uninstall, and talk to your child. It helps. There mostly is an uninstall-manual in the game box.