As the instructor, you make the decision. Never do anything that you are not happy with. What is the purpose of the exercise, is it acheivable in the circumstances? If your student has an issue with "more than a breeze" maybe a demonstration to show what can be done, but there is little point trying to teach him in extreme condiions. I have shown a student what a 40 kt wind in the circuit looks like and that a C152 can be landed with a 27 Kt crosswind, I would not have expected the student to do either and it could be a demonstration of decision making and why no to do it.