There are buses that run directly from Midd to Boston, South Station, every time there is a school break. My daughter took them every time. I think the cost is $40 round trip.
It is easy to catch a bus from Midd to Burlington. From Burlington you can catch a bus to Boston.
I think some students fly in and out of upstate NY also. I’ve seen that on the Facebook parents page.
Hopefully someone with more direct flight knowledge will respond. We live on Boston so it’s not an issue for us