Plato's ideal educational program at the Academy, was a program in which the study of mathematics, geometry, music and so forth introduced discipline into the students overall characters, and order into the mind. But to be a great teacher you need an abundant amount of knowledge. Knowledge is a range of information or understanding of what is known. Knowledge is also the fact or state of knowing and knowing is to have knowledge. A teacher of knowledge will teach facts, not opinions.
Opinions are an evaluation, estimations, a guess, or what seems true or probable.
Plato believed that if he could identify and articulate the differences between mere opinion and genuine knowledge, it would then be possible to identify the structure of the ideal state, a state based on knowledge and the truth rather than the mere appearance of truth and personal whim. You see more and more in today's society that people will give themselves a title without earning it. In Kung Fu or Karate, people will give themselves the high rank of a Master or Si-kung, without ever really acquiring the skills of knowledge to attain it. People will believe and trust these people because of titles. A great teacher will gain knowledge from no knowledge.