I also have the flip side of where I'm studying and looking after a house hold and raising a family and it's tiring and taxing, but I am doing it by choice, my teenage children wouldn't be.
My kids contribute to the running of the household (as does my DH), I just don't like the idea of having a teenager who is at school and very possibly working part time to be responsible for mowing lawns/cooking x amount of meals a week, cleaning bathrooms etc. on a regular basis.
I guess my parents did it well...when I was on school holidays and my parents were both working full time I'd surprise them by cleaning the whole house (minus my sister's room) for them when they were at work etc. I wasn't ungrateful...I didn't fully understand the full impact of everything my parents did for us until I became a parent myself, but I wasn't horrible and selfish.
I think it's very reasonable for the OP to expect one chore in the afternoon to be completed by the teenager...for me it would be more cleaning up after dinner, rather than cleaning bathrooms. I find some of the list of chores that pp have mentioned they had to do at the same age quite extensive.