But nearly all require separate applications with different deadlines.
District officials are now considering moving to a model called universal enrolment. It's already used in cities including Denver, New Orleans and Washington.
The process would allow students to rank their preferred schools on a single application. A computer algorithm would generate the best match.
The concept has met a lot of resistance in Philadelphia, one of the nation's largest districts.
Critics say the system actually reduces choice because it essentially assigns students to a school.
Supporters say it will streamline a patchwork system and make it easier for disadvantaged families to get information.