Rather than thinking of a teacher necessarily, one can think of an individual acts more like a mentor or coach in certain settings.

不必要一定要有个老师，你可以想成一个人在某个领域,作为指导者或是教练。

麻省理工公开课 - 媒体、教育、市场课程节选

As a teacher, could you give some advice to the students who are studying English?

作为老师，你能够给正在学习英语的学生们一些建议吗？

紧张是学英语的敌人 - SpeakingMax英语口语达人