For my DS, it was these factors and mutual respect. Most teachers admitted, one way or another, that they had not taught a student like him before, so they supported rather than tried to lead him. He followed the class routine as much as possible (which was really good for his social development) but they gave him a lot of room to differentiate the material.

Occasionally, when his regular teachers were away, well meaning substitutes would give him advanced or extension material which he would respectfully complete but then bemoan to me that they might as well have just given him regular class content as all the materials were so basic, so I got the strong impression that his regular teachers really did give him almost full autonomy.