Oscars grow real quick, so start thinking and get going soon on the new tank.
As for the question of where to keep him, if you keep him at home then you will have to do water changes every weekend you come back. Also measure the food out in little pots so your folks just have to pop the food in.
If you take the fish to your school they will be fine without food for a day on the weekend, also you can do water changes during the week (you are not stuck with doing it on the weekend). Until recently my fish only got fed for 6 days out of 7 (i give them peas now on the 7th day and some wont eat them so they dont eat), it does them no harm at all. In the wild they will regularly go for a couple days without food