Miluai Even says: When learning with a student, a person feels a need to be the giver and not the receiver. As a result, he must know the subject clearly. By doing this he learns with greater breadth and merits true understanding. In Talmud Tractate Niddah pg. 17 it says, "As a youth Rebbi was the student of Rabbi Yossi. When Rebbi got old he became greater due to his students. Rebbe was Rosh Yeshiva (head of the academy), and the Rabbis were often found learning from him, automatically sharpening Rebbi's learning.