It strikes me a bit like an upside down game of musical chairs.
Instead of the normal rules of musical chairs where players walk around while the music plays and when it stops they scramble to take a seat (with one less chair than the number of players), in the upside down game, the rules are that everyone starts the game seated in a chair as of May 1. When the music starts, a chair is added, and a player switches seats, thus opening up a seat for another player to switch. Chairs keep being added until the schools run out of chairs or until the players want to stop playing.
Not a perfect analogy, but still…