What special arrangement does freak make when he and Maxwell go back to school in chapter 12 is this surprising?

Freak makes a special arrangement with his teachers when he and Maxwell go back to school in chapter 12. He asks that he be allowed to attend classes with Maxwell, even though he is not enrolled in the school and this is surprising. This is surprising because it is unusual for a school to allow a student to attend classes without being enrolled. However, Freak is able to convince his teachers that he will be able to keep up with the work, and they agree to let him attend.