My daughter is 15. I give her an allowance of £50 every 4 weeks (12.50 a week).
This may sound like a lot, but she has to buy everything she needs from phone credit, clothes, going out (bowling & cinema), toiletries, mates birthday pressies, magazines, shoes etc. She has a packed lunch, but if she decides she wants to use the school canteen - she pays for it.
I decided to do this after a client of mine told me she did this for her daughter - as one week she cost me £20 for some tickets, £15 for make-up, £3.00 for a magazine & £15 to go bowling & £10 phone credit - all within a space of 3 days!!!!!
This way, she is learning to budget better & not be wasteful with her money.
She does have to do jobs around the house - if she doesn't, for every job not done she'll lose a £5 - not had to do that yet!!!!!!