There might be some information that could be combined with other data in ways that would violate the privacy of students and their families. Obviously discipline records with student names shouldn't be public, but what about records without names where the students name could be found by linking it with other data.

AOL released a bunch of search queries in 2006 with they idea that they were anonymous, but it turned out you could get quite a bit of personal information from them by linking searches together.

Most obviously, personal information about students.

Presumably all data about student educational outcomes, which are protected by FERPA. The school system doesn't have the option to just ignore the law and make this information public.

If you're curious, read up on FERPA.