FWIW, amid the talk about Raspberry Pis, the (fully open) BeagleBone Black/Green has a default experience for casual-tinker-friendly programming where it spins up an on-board Cloud9 instance for the user to poke around.

It's slightly more expensive than its Pi contemporary, but that's expected when everyone keeps flocking to the Pi and the alternative can't make use of the same volume discounts and self-fund engineering to put new board revisions out every year. And even for all that, it's a popular alternative—you're not left hanging out in no-man's land with some exotic hardware. Check the hackerboards.com surveys from over the years that show it trailing the Pi(s).

Eclipse's Che is also very interesting. I hate the name, but it was super when I tried it.

If I were teaching, I would definitely look at something like Cloud9. I'm in the process of going through Michael Hartl's Ruby on Rails tutorial based on Cloud9 and I'm blown away by how good it is.