It might help to get a rough idea of the usual going rate? I have 16 yr old twins and they get £20 each per month and the same from my parents. They buy their own snacks etc. at college with that and occassionally work at our family business at weekends, I very rarely buy anything but food/college essentials, if they want something that's more expensive ie. New football shirt etc. they get it for birthday /Xmas.
My dd is 19 and tried for ages to get a job with not much luck so volunteered at various places which helped her cv, she also got the same amount as they boys do now. I don't think it does them any favours to hand them money on a plate, a job doesn't have to impact studies - it's just hard finding one that fits around school etc.
There is always the option of car washing / selling on eBay etc. To Some employers seeing a work ethic whether paid or not is a huge plus point, the competition is higher than ever so it's not always about having the best grades, it's the whole package.
Whatever you decide though don't base it on what other parents (supposedly

) do , you are on a hiding to nothing when you do that
MFW 21
Target for 2018 £40k/£9,626 paid so far
Mortgage £39,159.44 -4yrs 2 mths left. Total owed £52,364 plan to clear in 14 months