Teacher is the one who is teaching. Student is the one who is learning. Thus a particular person can be student and teacher both of a given subject. Now, depending on the timeframe, dedication, quality and status of any teacher-student pair, it is possible that one of them is superior than the other in terms of knowledge. At one time, one may be superior whereas at another time another one may become superior. Therefore, a really good teacher does not suppress their students or does not consider them lower in any way. And, also a real teacher lets a student progress than the teacher.
Of course, when it comes to the final Self Realization, a teacher who is totally liberated is the most supreme. And, a student can at the most reach that level, but never cross it. Such a liberated soul is called Satguru.
There is a difference between Satguru and Guru.