The idea that students should write their own textbook is radical in the context of an authoritarian tradition of school teaching and learning. But once we accept that learning can be fun and involve play – and therefore that game-play can be educational – it is only a short step to understanding game design as meta-pedagogy. To play a game is to learn its mechanics and dynamics, and maybe to master it as a user. To create a game is to learn it from the ground up, and the inside out, which is far more challenging and – in direct proportion – rewarding.
Playing a cigar box banjo sounds fun, and could be a fantastic learning opportunity; but how much more fun (and pedagogical) would it be to play one that you had made yourself?