Thanks to the exposition of Internet, people can access to the vast quanlity of information on various fields. Therefore, the one who want to gain knowledge do not have to go to traditional school to study with teachers, he can do it by himself which is a way many people will choose.
Since teachers have plenty of experience and are the experts of certain field, they can help students gain the knowledge in short time. They can quickly identify students' problems and help them figure out valid solutions.

With teachers’ supervision, one can secure the rate of study progress. Teachers are likely to assign homework to make sure students master what they have learned in class and have a strict schedule. On the contrary, people who study alone are always having a hard time carrying on their original ambitious plans. When I learned how to swim, my teacher was very demanding and asked us to practice every day. Although it was quite painful to beat my laziness, I feel appreciate for her strictness to make me become a good swimmer.
 
Although it’s very convenient to study by oneself for the flexibility of time, location and material, studying with teacher is superior regarding to the result of study.