WTC and Sons Pt job

Hi All.
We are on WTC and our eldest son who is till at school has just landed himself a part time casual job. He has also received his national insurance number recently and given it to his employer.
He will only be working now and again covering sickness etc. But is also looking for something more regular.
But i am curious as to what to do about out WTC. Does him earning affect that at all? He is still at High School and then will be going to Tech for 2 years. Any help greatly received.. Thanks