I don't do allowances.
1. they began to look at it as their right to be given money every week no matter how well they did their chores and it made a lot more work and arguements for me.
2. they began to look at every chore as how much it earned them rather than how much it helped the family.
3. My nephew even bragged about his and became boastful about recieving money.
What I did:
I told them school is your job just like I have a job. Sometimes it is fun, sometimes not. You make good grades, you get bonuses, like most employees do. You don't get good grades, no bonus and the possibility of being fired (kicked out/failing/whatever).
So each report card period they got money. $xxxx = All A's
$xxx = each A, xx = each B, x = each C, 0 = each D, -x = each F.
They make decent grade or at least try, they get money, they fail with no effort, they pay me! LOL They learned really quick. They also learned to budget to make it last for 6-9 weeks depending on the grading period.
To figure out how much they get, I sat down and decided what their normal expenses would be per week and multiplied by the number of weeks. For us normal expenses were 1-2 x buying lunch per week, 1 coke and 1 candy while out with friends, 1 extra dollar just to have to save, and x amount for tithing. Tithing was their choice but I did show them it did not take out of their lunch money--I had accounted for that. ;-)
When I asked for a chore to be done, there was no more, "How much does it pay, it is her turn, I did it yesterday, why me", or other comments. "Yes ma'm" was the only acceptable answer. And I also had to make sure I mixed things up. I had the boys wash dishes some nights and had the dd mow some days. ;-)
Oh and I had a list of xtra work for them with payment. They could sweep the porch, vaccumm the living room, etc. to earn extra money for projects.
Good luck