I'm a fan of teaching people the wrong way first, then ask them if they can find ways to improve the situation, and only after that give the "best practice" solution.

Doing things the wrong way shows them why, asking them to try to solve it themselves teaches them under which conditions the issues present themselves -- this is actually the most important part, don't write 200 lines of abstraction just to work around the fact that you use a paltry 4 globals.