This is for when a bit older, but as soon as I got a full time job (I was 20), I had to start paying board. The more I earned, the more I gave my parents.
Then, when I was looking to buy my first house, my parents gave me a cheque for the total amount of board I'd paid over the 2.5 years. Totally unexpected and awesome.
Hoping to do the same for my DD in the future.