I have two. My son (college sophomore) works summers only; my daughter (HS senior) worked summers while she was playing club VB and is now working 4 - 5 hrs/day during the school year. She schedules herself and wants to work so she has some extra money.
They're motivated by different things, so I think the real answer is that it depends on the kid.
They're motivated by different things, so I think the real answer is that it depends on the kid.