Teachers are on their feet the majority of the day, and schools need to remember this point. Teachers should maintain a certain appearance. Male teachers should wear khakis or dress pants and a button down or a polo-style shirt. Female teachers should wear a nice blouse and pants/skirts. Requiring male teachers to wear a tie is a school's responsibility, but then, how do you distinguish a teacher from a principal?
Teachers should be able to wear comfortable footwear while at work, considering that teachers spend a large part of their day on their feet. Should teachers be allowed to wear tennis shoes? Well, that is what school districts need to decide. What about open-toe shoes? I would say that sandals should be allowed, but flip flops are a no-no. However, some "flip-flop" style shoes look more appropriate than some dress shoes.