Actually, as long as there is no local law against it, he can do summer work. Its not under the table for him, he is under 18, and technically, if he worked, would be due all his taxes back...?
As some who has had their own dog kennel, breeding areas etc, find people who need the lawns cleaned. You wont have to spend money on gas. Just rubber gloves and recycled grocery bags. And people will pay $$ not to have to pick up dog droppings!
If you live where someone raises horses, mucking out stalls is a good job that pays too. Look for jobs the average person does not like doing. Not sure where you are, but if near Simpsonville let me know.