I've never heard about this Secret Teacher column on the Telegraph before, so thanks for that! I've had student teachers in the past, and yes, it's a lot of work for the supervising teacher. If the student is good, then the classes roll very nicely without a lot of issues, but even then, there's still mentorship that takes place on a daily basis. If the student isn't that great, however... imagine trying to teach your classes, help a student teach his classes, and get prepared for fixing the disaster once the student is gone. Not fun. Being a teacher is great. Being a supervising teacher for a practicum student is... well, it's important to pay it forward, as I had fantastic supervising teachers while I was in undergrad, but it can be very, very challenging.