Hiya.
Corns are usually mature at three, but the critical factor is whether the female is at a suitable bodyweight (too small and she could have problems with laying/egg-binding). How much does your lady weigh? Are they both physically the same size?
I breed mine without brumating so I think it's a "nice to have" rather than a necessity (seems to improve fertility).
Bear in mind that Corns are most active at dawn and dusk, so your class might miss the mating anyway.
Make sure you monitor them carefully all the time they're together. If they've never shared accommodation before, you could find that they take a dislike to each other and you might need to separate them in a hurry. With any luck the mating instinct will rule, but better safe than sorry. One important point is also to make sure that they've both eaten in the preceding five days, just to be absolutely on the safe side.
I agree that the best time to introduce them is immediately after the female has shed - they seem to give off really strong pheramones at that point.
Also, if you intend to hatch the eggs that they produce, make sure that you have a way of selling the babes. The worst year for me was when I hatched 30 eggs, only for the dealer to back out and leave me with a lot of hungry mouths to feed.
Good luck - let us know how it goes and whether your class enjoy the lesson!