I wondered the same about a private class. Her comment was he needs exposure to other dogs to train him not to be aggressive! She spent most of the class helping that lady with her Doberman. Since there are two trainers in the class the other has the responsibility of working with the other 12!
Oddly enough, I have had this experience in other classes where an aggressive dog takes the bulk of the trainers time and focus.
My thought would be, have the trainer give private lessons using their own dog first. Let them work with other trainers dogs! Let them put their own dogs at risk first! Then, once the dog has shown an aptitude to tolerate other dogs and can control his outbursts, allow him into the next class with more dogs.
Maybe this lady is a friend of hers? She sat after class talking with her laughing and joking around with her. Certainly did not seem as if they were discussing the dog. The dog is a perfect specimen of a Doberman. Her is just gorgeous, huge with perfect ears and construction. Possibly she wanted to show him in confirmation but with his aggressive nature, there was no way that would happen.
I am at a loss to understand why aggressive dogs are tolerated. Just my 2 cents!
Thanks for letting me vent!