Manual labor.
And I mean HARD work.
Kick his ass into the ground building a fence, cleaning gutters, mowing lawns, cleaning bathrooms and kitchens with a toothbrush, detail your car, make him clear out the attic, clean the garage. Write an essay a day for you explaining his actions, reasoning, behavior and his plans to change. If he blows it off, he does it again. All day until he gets it and you accept the work. I had plenty of people telling me what I did wrong, it did nothing. Having me analyze myself and my actions was far more challenging to my reasoning.
Basically, this kids job was to go to school and learn to be responsible and accountable.
He fucked up.
His new job is to do every menial task you can think of – which if he continues on this path of unruly behavior and poor judgment is what he will be doing in the future.
Make it as unpleasant as you possibly can. You want to make him GLAD he’s going back to school and make him hate the idea of being suspended. Which as a kid, seems like a treat.
Some of those things, I learned after being arrested as a young teenager, they leave an impression without being damaging, reactionary or wasting anyone’s time.