bad times! i dont think a trainer should ever punch a student...if they need to get stern then harsh training is the way.
one of my mates knocked someone out too quickly in an amatuer bout once. he was meant to be using him as real practice and making it last a few rounds but he just dived in. he had to do his next training session on his tip toes. if his heels touched the floor (there was chalk all over the floor so you would be able to tell) he had to box a round with the trainer who wouldnt hold back.
he did the session on his toes and later found out (when he finished with the gym) that there was no way his trainer would have ever boxed a round with him.
he learned from it though...