When should parents request a 504 instead of a full assessment for an IEP?

If a student, for example, is a wheelchair user but has no other needs — everything's going well socially and academically, and they use a wheelchair for their mobility — that might be a situation where parents go straight to a 504 because the child doesn't need specialized academic instruction. However, they do need someone to make sure that they can physically access all of the places they need to physically access, such as the elevator, or they need to make sure that the teachers are aware that the desks have to be X feet apart. If there's a medical need, sometimes that goes straight to a 504. A kid who has diabetes, for example, may be doing well in all areas except that they need to leave class to check their blood sugar regularly, or go to the nurse's office to get insulin, so that potentially could be written into a 504.