Also, what does paid in flying time mean?
Well, one can guess by doing the sums.
If you're an adult minimum wage is around £5/hour (I think for 14yos there's no minimum, but it would seem reasonable to pay around the same if you get the same standard of work from a kid, I know people round here who do). Flying is around £150/hour (all very round approximate numbers these). So that would suggest that one hour's work might buy you around two minutes flying time, or work nearly full time for a week for one hour's flying.
But ... "paid in flying time" does sort of suggest some sort of "oh dear what a pity I accidentally seem to have forgotten to tell the tax man about this arrangement" sort of deal, so if you were otherwise on 40% tax (unlikely of course if you're earning minimum wage) and going to pay VAT on the flying that'd take it up to around four minutes flying per hour's work.
So, slog your guts out all weekend and get half an hour flying (which means twenty minutes in the air and ten minutes pissing around on the ground), assuming you're actually supposed to be at school during the week. That'd sound like a good deal to some people, actually; less fine perhaps for others.