Reminder that Rabu couldn't get a discount on the theme park, because she isn't a proper student anymore since she dropped out more or less. Drop outs live on the street since all your benefits in this society are linked to your school ID. Your money, discounts, your housing is all tied to your school ID.
While we see Aru using her school ID to buy ammo in the old art, which shows that Aru and PS68 are still proper students who are enrolled and passing school. For the few people that think PS68 are drop outs like the other gangsters. Gehenna standards are so low that you barely have to attend classes and you can still be passing. Aru is a model student.