Good question. Ya made me reach for the old reg book.
First, it's gonna be up to the Examiner, but, for fun, I looked at and compared the requirements of a CFI-A vs. a CFI-S.
At first, it looks like the CFI-S has to take the same FOI written, but it looks like the CFI-S does not have FOI in his required flight training.
61.187 (CFI-A) flight proficiency;
(b)(1)(i) Fundamentals of instructing.
Under 61.409 flight proficiency requirements for CFI-S do not list this requirement, and would not be testable (except that the Examiner can ask whatever he wants anyway) on the CFI-S, so it would be a requirement on the CFI-A
I'm just shootin' in the dark here. looking at the regs. I have no idea how it is in the field. No Sport airplanes in my neighborhood, but I am interested and always looking.