It is not true that Jesus is the only teacher. In fact, there are many words and many occurrences of the words teacher (59 times), teaching (51 times) and "I teach" (97 times) for a total of 207 times in the New Testament. For example, none of these passages are about Jesus, but rather those who are called to teach:
"Not many of you should become teachers, my brothers, for you know that we who teach will be judged with greater strictness. For we all stumble in many ways. And if anyone does not stumble in what he says, he is a perfect man, able also to bridle his whole body." James 3:1-2
"Having gifts that differ according to the grace given to us, let us use them: if prophecy, in proportion to our faith; if service, in our serving; the one who teaches, in his teaching;" Romans 12:6-7
"And he gave the apostles, the prophets, the evangelists, the shepherds and teachers, to equip the saints for the work of ministry, for building up the body of Christ, until we all attain to the unity of the faith and of the knowledge of the Son of God, to mature manhood, to the measure of the stature of the fullness of Christ, so that we may no longer be children, tossed to and fro by the waves and carried about by every wind of doctrine, by human cunning, by craftiness in deceitful schemes. Rather, speaking the truth in love, we are to grow up in every way into him who is the head, into Christ, ..." Eph. 4:11-16