M.S.
Hi X.!
My son is also in first grade and has some social issues with others to address. Remember, they are all kids and need help developing their social skills. My suggestion is to go to school just before the recess begins so you can see for yourself what is going on. My guess is your son likes some of the attention he is getting that is why he is playing that "you can't get me game" that the teacher observed. But, it seems like the girls have taken it too far. So, if you go and leave your other children with someone else so you can be attentive, watch from a distance. Don't let your son know you are there, and just see what happens. Often times we don't get the whole story from our children, only the parts they want us to hear. So you have to piece it together, look for the truth not just what you want to defend your son. There is no better way for your son to learn to interact with others than in the live fish-bowl of school. Taking him out will not give him the skills he needs to be adept at relationships and problem solving. I would certainly give the teacher a heads up of your plan, but I wouldn't let your son know.
I recently did this with my son over his food choices at the cafeteria, and although we had been discussing healthy choices, he wasn't implementing it. SO a surprise visit serves a purpose, and lets your kids know that you are monitoring and you care.
Good luck!
M.