Thank you for your input, BY, Faldage, and Bean. I think the problem is that the possessive really refers to the (singular) one, rather than the (plural) students. So in writing I'd have to go with Faldage's suggestion and avoid the problem, although I don't think it's something I'd ever actually say . Fortunately we don't have to worry about apostrophes when speaking.

Bingley

Bingley