We have an excellent student helping in our school, who seems capable of teaching a class. Can we allow him to teach a number of lessons, although he is not qualified?
Students on teaching practice are regularly given classes to teach as part of their training, with or without a teacher present. The decision to do this is a matter of professional judgment on the part of those responsible for a student's supervision.
The responsibility lies with the head, but, if all concerned are satisfied that this student is capable of taking these classes on, there is no reason why he should not. Proper arrangements for monitoring his progress should be in place.