After the bullying incident, I had to pick up a few books on body language. Unlike us, they lack this ability more than others and sometimes, they don't have any of these skills. I am making him read these books.
I am finding BODY LANGUAGE HANDBOOK by Gregory Hartley and Maryann Karinch really helpful. I hope you pick it up and read with your child. I am going through this book with him and trying to teach him the basic signals that he doesn't pick up on his own.