"Step on a crack, break your mother's back."
...a productivity game for walking to school.
Few kids walk to school anymore, so this game is probably less popular than it used to be. Just like Ring around the Rosy, there is an unfortunate history behind this one. (you'll have to do your own research)
An interesting observation about this game, in the context of walking to school, is that depending on the size of the kid, or more importantly, the length of their stride, this can either be an aligned game or an incidental game. An aligned game is one where the scoring is aligned with the goal and helps the player be more productive towards that goal. So a smaller child who must lengthen their stride to avoid a crack, this game helps me get to school faster and in fewer strides. If I am a tall kid, I might have to shorten my stride to win the game, and even though the scoring is incidental to my goal of getting to school, it is a fun game to keep me occupied during my trip.
In this case, to tell us about luck – but that assumes the game is not played to win – that it is "unlucky" to step on a crack, and not a deliberate action to avoid the crack.
Depending on how it's played, the "step on a crack" game could be an example of an aligned game or an incidental game. An aligned version of this game would have the sidewalk leading the way to school, and students playing the game on their way to school, increasing the speed or likelihood with which they arrive. An incidental version of the game has the game taking precedence over the route. Students go out of their way to find cracks to step on or avoid – independent of whether or not they are en route to school.