Can I use my pending i485 to go to school as a local student?

You are lawfully present in the U.S., where there is a pending adjustment, but if the adjustment is denied, you may find yourself out of school.  As a result, some private schools are more sensitive than others about accepting students who's immigration or visa status is in limbo.  There is no indication that they will be lawfully present by the time of graduation!   Do you have an employment authorization card, yet?  Admissions tend to rely upon F1 non-immigrant student visas as the better option, but you can't get that if you have immigrant intent!  Check with the International Student Office to see what admission policies are at the schools to which you want to apply for admission.  Some State schools are less restrictive about alienage than others due to restrictionists in State Legislatures who are upset with foreigners who were once unlawfully present.  As a matter of law, you should be allowed to enroll, but can be denied admission as a matter of discretion.  For more information, seek a consultation with an immigration attorney more experienced in these matters.