And if you _don't_ randomly assign, the effect is even stronger: students who are being well served by the standard/control school don't opt to change, while st

And if you _don't_ randomly assign, the effect is even stronger: students who are being well served by the standard/control school don't opt to change, while students who aren't are primed to jump as soon as the option is provided. So the alternative/trial school gets both ends of the bell curve on almost every metric (the main exception being athletic performance, since the larger school typically has more team sport options).