Is your son strong enough to hold him if he decides to behave like this? You could be unintentionally be putting your son at risk of being dragged along if he isn't.
Many dogs won't work for treats but will work for something else, a ball, squeaky toy etc. it may take some finding but worth the effort.
No, he's definitely not strong enough to hold him -- I'M barely strong enough to hold him, as I've been dragged to ground a few times already!
After that incident my son agreed he won't be taking the leash until we get things under control, but he participates in other aspects of training and care -- he feeds him, helps train him in the house, and throws balls outside in the yard while I keep the dog on a long line.
He's making progress on our walks. We have A LOT of dog walkers in our neighborhood, so it's tricky trying to avoid them at any time of day right now, but for the most part I've been avoiding other dogs if I can spot them in time. Gordon (my dog) is pretty good now at turning around and walking with ME (rather than trying to go back, pulling the leash to get to the dog in the distance, etc.) if I can turn him around while there's still a good distance between us.
I've been working with him on recall during our walks by using squeezy cheese (thank you, whoever suggested it!). He's becoming pretty good at stopping and coming back when I call him back -- so much so that yesterday I had to stop to scratch an itch on my leg and he stopped and came back to me! ha ha!
I'm slowly learning where his threshold is for reactivity, and if a dog comes around a corner where it's already too close for me to turn in another direction, I try to get his attention quickly if I can. Sometimes yes, sometimes no! If no, I just keep encouraging him to continue walking with me (while he's jumping and lunging the whole time).
Definite progress, though! The last two days he's done better, and then last night's walk was mostly an exercise in frustration -- for both of us. The weather cooled a little and the humidity went down and I think EVERY DOG and EVERY CHILD was out and about last night!
Baby steps ...