Mineways is a free program that lets you export your Minecraft creations into models for 3D printing. It's really easy to use! My IT department downloaded the software onto our computer lab PCs and we were good to go.
Here's a brief tutorial on how it works:
The day of the program, I start out by opening up Minecraft and going over what all the options mean in Mineways. The nice thing about Mineways is that a lot of the 3D print configuration setting are done for you. So you really don't have to mess around with it too much unless you want to. To create my outline, I used this page (scroll down to Export Options).
Then I let them take about 90 minutes to build something in Minecraft (on creative mode, single-player, though you could let them partner up to build something together) and upload it to Mineways. Then I save their prints to a flash drive with the file name as their first and last name so I don't get them confused. I let the teens know that it will take a few days for their prints to be ready to pick up.
How It Went:
The program itself went really smoothly. I was able to walk around and help the teens with exporting their designs. We created a shortcut to a free .stl preview site so teens could make sure their Minecraft creations would translate well as a 3D print. If not, they could then go back and fix their design.
Depending on the 3D printer you have (we have a MakerBot Replicator 2), you may have to warn your teens that it won't print smaller, more detailed things from Minecraft like fences or flowers, even if you choose to "Export lesser, detailed blocks" and it shows up okay on the .stl viewer. I had to call a couple of my teens back in to redo their designs because they wouldn't print correctly.
Have you done a Mineways program? Or have you used a different program, like Printcraft? If so, how did it go?