I would try one on one interactions and play dates first before trying to tackle group settings. It sounds he has had many negative group experiences and may need a self-esteem boost with some one on one interactions. He can focus on building a friendship, gain some confidence, and get some experience under his belt interacting with others. I would also reinforce that nothing is wrong with him and encourage him to continue to be himself. I hope this is helpful.

Amber

That is a great suggestion Marklinsmomma had. The one on one are much easier for many kids. Groups can be hard to navigate and when one child turns mean/critical in a group, it's easy for others to follow suit. My oldest son has had some of the same issues and he is 13 now, really big, outgoing and athletic, just aimed to hang out with a group of kids that don't seem to have room for him in their clique. He has spent time one on one with some friends and made strong connections with some. It all came in time, over the last 5 years. It wasn't overnight. And there are some that will probably exclude him forever because that's how they have learned to be from their parents.
I work in a middle school. Kids have cliques and nothing is going to change that. I try to tell my kids to be open to being kind to everyone and when my kids find other kids that have similar values they connect. Also, that we all connect to someone, and we never know who it will be. Sometimes it's not who we think it will be. Surprise friends come right out of the woodwork all the time.
I tried to de-emphasize the situation when my son was feeling left out. I knew if I fed into it he would turn angry and really withdraw from the other kids altogether. If the other kids didn't invite him then I'd say to him "that's okay, we have plans, anyway" and we'd do something as a family - which is very common for us to do.
You also said that your son is very polite. My son was like that too, as he had done homeschool and then went to enter public school. Some kids were way more crude than he was. To make matters worse, he entered a scene where kids had gone to school together since they were in diapers. My son was looked at like an alien. In a small town many people, I've found, don't know how to meet a new person! HA! Very closed minded. It was shocking to me since I'd traveled the country and spent my whole life meeting people.
Don't lose heart. There will be successes and set backs in his social life for years to come. One good friend is all anybody needs. I see the most awkward kids in school be totally happy and content with life because they have that one amazing friend, their comfort zone. That always makes my heart soar.

Sunshinenshowers,

What great helpers that have replied to you, I know that I will use their advice if we experience what your son is going through. I just wanted to elaborate more on what winterblossom added. I was taunted in grade school because I had curly hair, I never even reacted much to it except to feel that these kids were really immature. I can tell you that what helped me overcome my feelings of awkwardness were my parents constant positive re-enforcements of what they thought of me along with having mom outings that just made me feel great love. Today I look back and feel that my brother and I were the most important people in my mom's life and she sure showed this. Building up your son's character with all that you have to give is a great combating resource for his current fitting in issues as well as any life issues. Please keep us posted on how your one on one experiences go, I bet they will help both you and your son. Also, think about boy differences and girl differences. I tend to think that my fellas need talking and relating type things with friend, but they can relate through being at a park with one friend even if they say 2 words to each other. This is a funny thing that I have noticed over the 6 years I've been a mama.