I would push hard on the idea that he can walk across the football field without needing supervision.
It is possible the EF issues may come into play? That said, there may still be room to successfully negotiate for the child to walk between buildings. The waiver, window, and cell phone are all creative approaches. What about having the child accompanied by an aide (especially if that would be part of the EF IEP/504)?
In most school districts, students who live closer than half a mile or a mile away do not get a school bus, and are expected to walk to school. Ask why it's ok for the schools to expect him to walk a mile to get to school, but once he's there, he can't walk 100 yards.
It is great to ask and have the school articulate their position, as then parents can work on overcoming objections. In the meanwhile, it may be safe to anticipate an answer along the lines that the school is not responsible for how a child arrives (car, bicycle, walking, etc) but is responsible for the child on school property, while school is in session.
