There is a workaround where teachers can access any report card (students that are not in their class) early before it is public for parents. They switch to the Faculty persona, then head to the Student Directory and search for a student. When they find a student, they click their Contact Card and they have access to the Progress tab where the report card lives.

Thanks to Blackbaud support for showing me how this works.

This is a problem for pretty obvious reasons and needs to be remedied.