It's understandable that your teen is hesitant to go back to school if they are being bullied.  Have you and your teen talked to school administration about they bullying they have experienced?  If not, it's a good start to speak to an administrator.  You may also want to consider having your teen talk to the school counelor for advice on coping skills that will help them deal with bullying during the school day.  

If your teen is being verbally bullied they don’t have to listen to it.  Have them think of a few quick comeback lines they can use such as “ok” or “I’m working on that.”  Have them say something that doesn’t have emotion attached to it, and something that the bully can’t argue with.  Their other option is to simply walk away.  If they are in a situation that they can’t walk away from such as during class in school, ask the teacher if they can move seats, or tell the teacher what’s going on and ask what they can do to help.  If they are being bullied via texting, or internet sites such as facebook, or myspace, they can restrict certain people from getting on their profiles, and they can also restrict certain incoming phone numbers on their cell phone.  If they do find a way to send a message, simply ignore it.  The more your teen fights back, the more fuel they're adding to the fire.  The bottom line is………..ignore what they are saying or doing and remember that the bully is not better than them.  

You mentioned that home schooling is not an option.  Are you willing to look into sending your teen to other schools?  What other activities outside of school can your son get involved in that will help build their self-esteem and give them positive reinforcement?

Sometimes it helps to talk to someone about the bullying they've experienced.  If they don't feel comfortable talking to the school counselor, we encourage them to call our teen crisis line.  We're here 24/7 and it's free to call.  Our crisis counselors can be reached at 1-800-448-3000.  

Boys Town National Hotline
1-800-448-3000

Most people consider "changing the school" is a bad option for bullying. However, I totally disagree. Common sense tells parents to get the child out of that environment as soon as possible. There is no need for your child to be bullied. If I was you, I would not completely throw homeschooling option out the door. There are many teens that homeschool while parents work, etc. and it works. HOmeschooling is not like your typical day at school. There is a lot of time wasted. And it you will also find that the rigorous work loads at school are really not needed for the same results. Its a new world when you choose this and very free. I believe its better for any child who has parents willing to think outside the box.
in addition, your child's self esteem has been bruised. So it needs to heal :) Check out your local churches for youth activities that build self esteem. Also, the Girl Scouts and Boy scouts offer teens many leadership roles and activities that build self-esteem. You can also help by taking some extra time out of each day to do something that is productive and constructive with your child. Passive activities such as watching a movie do not play have the same effect as an activity that takes time, energy, effort and thought. Maybe get the child to start a local anti-bullying organization. He/she could speak out on the topic and develop a support group that would help others all the while helping himself. Take his or her ideas and run with them! You will be amazed at how your child becomes confident again ;) Search local/internet contests such as science fairs, writing contests, etc. to also boost the esteem.

PLEASE avoid beauty pageants and things that are artificial in nature. These contests only add insecurities to teens instead of  a sense of self worth.

Good luck ;D