While Gamestar Mechanic isn’t really a fit as a development tool for my course, it’s an excellent example of a teaching game, and I would highly recommend it for anybody with a middle-school aged kid (I think that is the right age range for it). The game is structured as a quest to learn to be a game developer, but what surprised me was how much of the focus was on good design, not just how to place blocks and enemies and make things go. You start out by just playing the various types of games that might get built (e.g. platformers versus top-down maze games) and becoming familiar with the differences, but soon you start getting walked through design concepts like how to use space or how to balance goals by playing the same game multiple times with a single aspect changed to see the effect. I loved the “quest” where you get to see how balancing a countdown timer and number of lives can lead to different types of game play. Overall, there’s a lot of showing not telling.
By the end, you can start building and sharing your own games in their “Game Alley, play others’ games, and it looks like there are occasionally challenges with prizes. The site does have a premium paid section as well as the free section, which may bother some, but from what I saw you can get a lot of value out of it for free – it’s not like some sites where you’ll find yourself almost immediately coming up against the limitations of what you get without paying.