My only knowledge of boarding schools come from movies and Harry Potter movies

I dunno then what real-world statistics are for them vs living at home and attending public/private schools. I would think though at 14 it'd be a major trauma that screws him up for life. If not from a culture that routinely does the boarding school thing, throwing a kid into that world and system is going to cause problems. And if he's already giving in to peer pressure trying drugs he's going to be exactly like that but without parental oversight as being away from the safety and security of home n hearth removes any self-control he may be exercising and he then acts out doing whatever's available to him there.
In the big scheme of things, it could be much worse than alcohol and pot. We've had more than a few Presidents into that and they turned out fine one might say heh (plus when parents drink or smoke or do drugs yet deny that to their children it becomes extra difficult coming down the mountain about it. If you don't want your children smoking, drinking, or trying drug ya better not be doing it yourself. Loose a lot of command authority if you're a hypocrite, and kids know what a hypocrite is even if they don't yet know the word.) If it's really a thing you feel the need to end, end it. You're the parents, he's the child. If you're all unclear on the relationship thing I suggest family counselling or a book about parents vs children. But hiding from your roles as parents and authority figures sending him off somewhere is more about you and your problems than his.
"I'd rather be hated for who I am, than loved for who I pretended to be." - Me.