First of all it's a physical eduction teacher, gym is the room we teach in. PE majors take a variety of science classes such as chemistry, physics, anatomy and physiology. They must also take exercise science along with methods or "how to" classes. Many different sport classes are taken as well as the education classes necessary to teach.
A gym teacher not only supervises track and field, but also conduct classes in nutrition. To become a gym teacher, you need a four-year degree. Here is a link to find out more information: