The real question here is whether or not the ban on clothing that I emphasized above is being enforced as rigorously as the ban on Confederate flag adorned clothing is. If this is true, then it would be hard for me to see a problem with the ban, as schools have an obligation to maintain order and discipline in the classroom.
Of course, having issues with the school dress code only helps to make the case for being allowed to redirect one's school tax payments towards private schooling that would allow for the clothing in question instead, i.e., more of a free market in education.
Wear a Che T-shirt and see if a similar ban is made.
http://thechestore.com/
How about a Lenin/Soviet Flag Shirt?
http://t-shirts.cafepress.com/item/lenin-soviet-flag-long-sleeve-tshirt/70334396