What was the context here? Was this in a group class where you saw the same dogs every week?
The classes that were for dealing with the reactivity were individual classes (with another dog for helping), although he would still see some other dog students coming or going at the training camp at the beginning or the end of our individual classes. Some of them we see often, some we never saw before.
Our trainer also provided a few sessions in which we walk together along with another student dogs.
Also, he would have our dog walk pass reacting dogs that are inside of fenced yards, sometimes too closely in order to train our dogs to not to react to them (which in this case I think that it's not a really good thing to do).
After seeing our dog reacting much less, and that he even showed friendliness towards some dogs in the training camp whether he had met or not (which is the product of the gradual approach as there were interactions, and not the product of forcing him sitting next to other dogs but not allowing interaction and only focused on punishing any reaction), we started group classes.
Since the training was not helping him to improve his confidence in other dogs anymore (since we've started to worry more about repressing, and then in the group classes we would do the same exercises regardless the progress of each dog), we decided to drop them. We don't agree with a lot of the trainer's ideas anyways. Now I'm contacting a positive trainer that would not need to use physical punishment and that really allows more dog-to-dog interactions, which is what he really needs and not just repressing.