Honestly, your son sounds completely typical and normal for a 3 1/2 year old boy of today. I was a daycare teacher for more than a decade, I've seen just about everything, I know how the system works, and it sounds more like his teachers have the problem, not your son.
I actually think it's pretty clever of him to try to trade toys with the other kids. In my opinion, that shows that he cares about not offending the other kids, and that he cares about their happiness too.
Of course, you want
him to interact and share with the other kids in his class, so yes, work with him on that.... but the reality is, at that age, kids are just
learning to play together and really don't start playing together
until they're more into their 4th year.... the exception being those with siblings, as they are constantly with other kids, they learn a bit earlier.
I completely agree with what ibake&pray said when she said, "Personally I feel that we push our children to mature too fast. Where is the time for gazing at a bug in the grass or staring at the clouds or watching ants make a trail. Childhood is a wonderful time of mystery and wonder and learning...let's not destroy this by pushing them to grow up too fast and too young."
The standards our society has set for our children today are just ridiculous and they do not allow for our children to be
children! And people wonder why teenagers are so completely screwed up these days..... sorry, way off topic!
The point is, your son doesn't need therapy. He doesn't need any sort of intervention. He just needs to be allowed to be a child. What you can do as his Mommy, is give him clear boundaries, consistent discipline, and lots of love and he'll be just fine.