Ok, who runs the school? Aspira, Excel, etc... Many alternative schools are still in some sort of partnership with the state. In that case it'll be easier to fight the system. If they are a private, like the 2 I just mentioned, There might be a harder to fight legal way around it. My girlfriend works for Aspira, and they are more tolerant even with the teachers. On of her coworkers even has a mohawk. But Excel tends to be much more strict. Their students walk in the hallways in silence, hands behind their backs. It's verymilitaristic there. It's necessary for their students though, and works wonders.
Even if it is hard to fight, it's never impossible. What you need to consider is what your locks mean to you. Are theytruly a spiritual/religious gesture? Most people with locks find that they do bring out some sort of spirituality in them, but their locks, themselves, were not grown for any particular reason such as that.
Is keeping your locks worth the time and expense of talking to a lawyer and working out the legality of your situation? Yogi Sunshine may not have locks yet, but does bring up a valid point. Education is VERY important. And your hair will always be there when you get out of school.
That being said, If you are seriously growing locks for a religious/spiritual reason, and not just going to claim it so you don't have to cut them, then they are protected under the first amendment.
I'd like to know more about who owns your new school. I'll look into if there are any laws/ dress codes they may have.
There's a good chance that the principal might just be very conservative and doesn't like long hair on guys.