From memory, the good old 172s are approved for spins when operated in utility category - max 2 people and limited fuel - fine for a lesson or flight test. You'd image this was done by Cessna because spins are required in US CPLs and it would be embarrassing to Cessna if you had to use someone's else aircraft for the flight test!
So really no fuss for those schools with Cessnas. For the other schools, logically an incipient would be anything between a wing-drop and fully developed auto-rotation - no reason not to take the stall right up to the wing drop and show sensible recovery using rudder. The important bit is that the student doesn't freak-out at the uncommanded wing drop, and tie the thing in knots using the aileron.