Ahh, well i was 15, 3 years ago, so not that long ago..
Personally, my mum said she'd do the same system, as you, because it was getting too expensive to give me money everytime i askd.. but told me to make a REASONABLE case for how much i think i needed and what i was going to get out of it, and what she'd buy... and to present it to her..
so being the teenager i was i made a silly case, then she told me to revise, then i decided i wanted to get my clothes, shampoo, lunch money and everything out of it, and i said how much things would cost, she sat down with me and we worked out how much i REALLY needed for each thing, and ended up with a much more reasonable amount and that was it, she didn't let me put things like shampoo in the trolley when we went shopping, if i wanted to spend more on certain things, i'd end up loosing out on other things..
She also said that i was EXPECTED to do certain things, as my household duty, not to get money, but because it was part of growing up and if i didn't she'd deduct money..
personally i thought it was a good system, because we agreed the amount together, we agreed what it would cover together, and i realised that if i did something wrong, or didn't do my part for the house, then my mum didn't have to do hers, and i lacked more and more by being lazy
xxxx