I'm wondering if enforcing hair styles as a part of a school dress code a new thing? I remember lots of people who I hung out with would be dying their hair all sorts of colors. That or huge spikes that were made with elmer's glue standing up all different directions on their heads. My hair didn't dread....but I went all senior year without using a brush on my hair once. It might be dependent on where you live but I've noticed a higher acceptance of visible tattoos and piercings that are allowed to be worn by employees. Unfortunately I'm out of touch with the current generation of high school students and what is the norm for dress code and how strict it is all being enforced. A lot has changed in the 12 years since I've graduated high school.
I say if you want to grow dreads...do it. Let them come in naturally. If they try and punish you for your hairstyle choices maybe see if you can get the media involved? If you are keeping your hair clean and washed, and over all good hygiene why should your hair in it's natural state be a distraction? How is it any different than someone who has super curly hair who may get just as much attention? How is one ok but not the other? It's discrimination.