When you say you corrected Xander for his reacting, what did you do?
Also, again, in the beginning it may be too much to ask your dog to sit
while another dog goes by, esp if other dog is close by.
For me and my dogs, I would just give the treats any time
you see the other dogs just to create the association that seeing other dogs is wonderful! Eventually you can shape the behavior into a sit or lay down or something more challenging.
Like today, I took Puma to Lowe's (huge hardware store) to practice our manners, etc. We saw another dog there and I took her to see the other dog at a large distance and immediately started giving her yummy chicken as I talked to her about how cool the little black pug dog was, etc. Soon she was laying down casually next to me watching the dog and eating the treats. In fact the other dog actually passed right next to as we were sitting down and no reactivity. We let the dogs say hi to each other and Puma was super gentle to the little dog.
But this has taken us quite a while to get to this point. Lots and lots of practice in many, many different places. And lots and lots of yummy food bites and happy chat
So much fun for both of us today practicing our manners at Lowe's--- esp since we kept getting so many nice compliments on her polite gentle behavior
So much fun that I ended up losing track of time and ending up being late for work! Dog training is so addictive.....