The more I walk, train with, and play with Ellie, the more I am convinced that encouraging your dog to play with other dogs is suicide.
For months now, I have watched how different dog owners interact with and respond to their dogs, particularly when there are other dogs around. There are essentially two groups:
This group usually takes a ball or some other aid out with them. They don't talk to other people, they play with their dog, talk to their dog, and train with their dog. They are there because they want to be there, and they value the time with their dog so much that they don't like sharing that time with anyone.
This group relies on finding a stick or two to throw for the dog, if they have to. Though it's more often the case that they just let their dog off leash, and expect any other dog, that happens to be in the field, to be a playmate for their own dog. Usually, they're more interested in keeping warm or dry than they are in their dog. All they are bothered about is doing their duty - walking the dog.
Now, there's nothing really wrong with either group, per se. However, how these groups behave does have a direct influence on how their dogs behave.
The first group, in my experience, have exceptionally well-behaved dogs. The dog has learned that the owner is the best fun. It's learned that, even if another dog runs right by it, it's never going to be as much fun as its owner is, and it will never throw a ball, day after day, whatever the weather. The dogs belonging to this group usually walk well on the leash, respond well to commands, and are focused on their handler. This isn't by accident. It's come about through regular interaction with its owner.
The second group, again in my experience, has the dogs we all dread meeting. It will run up to you or your dog, without any warning. If you throw a ball for your dog, it wants in on the fun too. And why wouldn't it? Its owner is boring it to tears. It's just a shame that you have to pay the price for that boredom. These dogs generally have a poor recall, because they have learned that other dogs are way more fun to be with, even if they're not a direct part of that fun. The owners of these dogs can't understand why you don't think it's great that they let their dogs interact and "play with" your dogs. After all, dogs love to play together, right?
Why am I writing this? I am writing it because I strongly believe that allowing your dog to play freely with other dogs is training suicide that you will ultimately regret. I have yet to see a single case that could make me change my mind on this particular issue.
Maintaining a dog's attention is one of the toughest things that any dog owner has to master. It's really tough. Once you start teaching your dog that other dogs can run faster than you, have no time constraints like you do, speak the same language as they do, and have far more energy than you do, you're on the slippery slope to moving into that second group of dog owners. Once there, no matter what you try to play, no matter what you try to train, all it will take is the presence of another dog, and your dog will be running off to play with it.
Do yourself and your dog a huge favour: use training classes for socialising, not your dog walks. Socialising, as far as your dog is concerned, should be no more than walking past other dogs confidently, and without pulling at the leash trying to play with it.