Hi M.,
I had similar problems with my son being bullied at the same age, although at least I didn't have to deal with a hostile administrator. Instead, I had to deal with administrators who didn't care, and wouldn't help. I finally used the school directory to call the parents of the main bullies and let them know what their kids were up to (very nicely). Three of the 4 parents promised me they would speak to their kids, and they stopped bothering my son. The 4th parent felt that my son was part of the problem, so the four of us (me, the other mom, and the 2 boys), got together for a little adult mediation. We gave everyone a chance to speak but not to interrupt, and no hostile language was allowed. We insisted that the boys use formalized mediation language that always started with, "I don't like it when xyz happens to me." They were not allowed to use blaming language, e.g. "You always do xyz." See the difference?
We got EVERYTHING out on the table and got the boys to work out their differences. It turned out that my son was engaging in inappropriate behavior to get the attention of the other kids because he was lonely and having a hard time making friends in the new middle school. After coming to this understanding, the boys decided that they'd like to try hanging out together and eventually became good friends for a couple of years.
A year or so later, we had similar problems with kids bullying our son at sleep-away camp. That didn't work out too well, unfortunately,as the camp administration was not willing to talk with us and were not willing to really deal with the problem appropriately because the other kids came from very wealthy families who donated to the camp, and my son could only attend with a campership. We realized, however, that our son simply didn't know how to deal with bullying behavior in an appropriate way, and made the situation worse by reacting to the bullie's actions (if a bully knows he/she's getting to a kid, the bullying just gets worse). Since bullies abound in all walks of life (even adults can bully each other!), we felt it was important for our son to learn how to modify his behavior so he could deal effectively with these personality types. We found an excellent counselor who worked with him for about a year, after which he learned how to stand up for himself in a constructive way. He hasn't been bothered by bullies since.
I understand your frustration and your need to protect your son, but I'm not sure pulling him out of the situation totally will be the best for him -- it might only teach him to run away from his problems, rather than teach him how to stand up for himself in an appropriate way and solve them. That being said, I would look for a different school that has a sincere zero-tolerance policy on bullying. This boy needs to learn good socialization skills, and that may not happen in a home-schooled environment. But, if you do decide to home-school, look for a home-school club with kids his age to provide social opportunities, preferably with plenty of adult supervision. If you keep your son in his current school, you might ask the administration if you could work as a volunteer aid in the classroom or playground to get a first-hand view of what's going on.
I wish you the best of success with your son, whatever road you decide to take. Thank God there are angels like you in the world who have so much room in their hearts to provide love and stability for abused and neglected children.