I don't know what they taught you in your dog socialization classes, but when I brought Bacca to puppy school, it was very much all about how to interact with other dogs, cats, interesting smells, distractions, etc.
Your trainer may be correct that the particular school you Darla too did not do the basics. If its all play, then she is definitely correct.
The socialisation group is at the vets and yes, it's all about play, no training. I noticed tonight that all the pups charge around playing and paying no attention whatsoever to the owners, even when called. Even Darla tonight ignored us twice when we called her.
Oh dear, I have taught her dogs = free for all play, haven't I?!

He'd snap at her in a New York minute and it would be appropriate behaviour on his part, it's funny I have had a couple of people actually thank me (mortified as I was, because I knew their dog wanted to be friendly and play, but sheeesh don't run into my dogs face, lol) but they said thanks so much as they needed a dog to tell their dog off. Toffee doesn't fight, unless the other dog just doesn't leave his space, he snaps and growls until they do. As soon as he has his 'purple bubble' back in place it's good again, lol!
. We were very fortunate to be able to adopt an adult GSD who is very much a no-nonsense dog and has very low tolerance of other dogs. Izabelle immediately taught Mozart to keep his distance and approach with care...but I didn't want him to develop a fear for all other dogs either so I got him enrolled in agility class which is grouped by skill level and not age so that can give your puppy exposure to adult dog of different age and size.