Everywhere you look in today’s society you see the role of specialists. They are everywhere from schools, to businesses, to sports, and even in Churches. Schools use specialists to teach a specific area. For instance in early elementary school a specialist, trained in Early Childhood Education, will teach the same students all day. That specialist is trained in imparting Early Education skills into young minds so they will be able to grasp knowledge in the later grades.
As the kids grow, the students begin to change classes in order to sit under different instructors who specialize in a particular area. As a rule, you do not see an English/Literature teacher teaching Algebra. In College we see this further demonstrated, especially in Math and Science classes. A Calculus professor usually does not teach Geometry, etc.