I have fairly strong feelings about this because my mother (single mother) made me get a job as soon as I turned 16 and I've fully supported myself since I was 17 (rent, food, clothes ect..) I naturally focused on the 40hr work week instead of school. My children will not work during the school year, they can and will be encouraged to work during summers depending on their sports schedule. However we tell them that their job is school, and given the homework load I'm seeing in Jr High I can't imagine they would have much time in high school either. I also won't compete with a job during school breaks because family travel is a priority for us.
Our oldest (almost 13 eek!) gets $10 a week or if I give him a $20 it's for two weeks. This is solely his spending money. We cover school lunches, sports, camps, clothing ect.. fully. Our 9 year old doesn't really get much cash because he is with us most of the time. If he goes somewhere fun with friends we offer to pay his share.