Hugh Jarse, whilst I agree with you in that in most cases the student is flying the aircraft, surely it is up to the instructor(when onboard) to ensure correct distances etc.
If there is no instructor onboard, then,IMHO, he has failed in his teachings of circuits/circuit emergencies, because the student is not performing the circuit correctly.A student cannot be blamed for the instructors failings....at some point in his/her professional career, the instructor must stand up and say..."do it properly"