Please don't take offense to this because I am not trying to start anything, but... how does paying for their gas and insurance set them up for the real world? I mean, they aren't always going to have that so it's not all that realistic?
I look at it this way. Their job right now is to get the best grades they can, stay out of trouble and to do their best in whatever sport or other school supported activity they choose.
If they were not each on 2 teams & getting good grades (easily a couple hours of homework each day & earning college credits in HS), believe me they would be working and paying more of thier bills or doing without a car all together. They spend anywhere from 2-5 hrs in the water depending on what part of the season it is. It is their choise to participate in sports. During the summers, they have jobs or lots of sitting lined up. I see this approach as helping them develop thier own strong work ethics to be successful in life.