The prerequisite for this to happen is that the school removes all physical editions of the books and has digital editions for all content, and a lending program for the books that is sufficient to satisfy publishers... and all students have digital book readers able to access the school library.
I don't see this happening in the near (or even within the decade) future. There is far too much content that is physical only, publishers haven't embraced digital editions for libraries, school libraries don't have the technical resources (physical or in many cases human) to convert their collections to digital.
The hypothetical school book ban for digital editions is needlessly alarmist.
When those resources are available to schools, then yes - lets talk about it... though the school banning books will continue to mean "that resource isn't in our collection" and a student can go to another library (or in many cases book store) and get a copy of that book for themselves. This is no different than today.