Some school districts are K-8 or 9-12 only, which I've experienced myself. Taking California as an example: https://en.wikipedia.org/wiki/List_of_school_districts_in_Ca...

> In California there are 560 Elementary districts, 87 High School districts, 330 Unified districts.

(I do think that this isn't a great argument against switching to DST permanently. I think if this was legislated then the school districts would just adapt now, especially since a significant chunk of students are still doing remote learning.)