If you or he lives in a state that offers a 529 with a state tax benefit (such as a deduction or a credit) and that state doesn't have anti-rinsing rules, then what you can do is open a 529, put in $X, turn around and take out $X for qualified expenses the next day, and then take the state tax benefit on your or his state tax return.
My state (Idaho) is currently one such state, and I did precisely that when I was getting my graduate degree. I'd put in a semester's worth of expenses into my 529, leave it there for a day or two, then take it back out and pay for that semester's qualified expenses. At the time the top tax rate was about 7% and contributions counted as a state tax deduction (up to a certain dollar amount per year), so I basically got a 7% discount on my graduate degree.
Some states realize that some people do this, so they have implemented laws or rules to try to prevent it.
529s can be a bit fee heavy, so you'd want to confirm that fees aren't bad. Also, most state 529s probably have the equivalent of a stable value or money market fund in them, but you would want to make sure that the money wasn't put into anything volatile.
Also, 529 distributions can only be used for certain things. You'd probably want to make sure that whatever you were contributing were not more than (a) the state tax benefit maximum, and (b) the qualified expenses your son will have.
And FYI you or he can establish a 529 for you or him. And you can have multiple 529s, so if the state tax benefits are significant in both states and the amount of assistance you're providing is large enough, you could do a 529 for him in your state and he could do a 529 for himself in his state.
