So, after he bit and wounded the other dog, did you and the other dog's owner exchange names and phone numbers? Is the other dog going to have to go to the vet? If so, did you offer to pay for the bills? The only reason I'm asking is because it seems more likely that she will report it and be hateful about it if you didn't offer to help. That's how a lot of people are, and, I'm just curious what you and the other owner did and/or said after the attack. I would tell Rex's instructor, though. I mean, he should know, that way he's able to make his own assessment on whether or not Rex should be in the class. Maybe he could do one on one classes with you. I don't know what the laws are over where you are, but, maybe (just to prevent something like that or something worse from happening) you could put Rex in a muzzle when you walk him. I'm sorry that that happened to the little dog and his owner and to you and Rex. That's scary on both sides! Let us know what happens.