What are the reasons behind the differences between the way teachers speak to students, the way friends speak to each other, the way parents speak to their children, and the way couples speak to each other?

Is the role of an educator confined to someone generally more experienced and wise (normally older); can't two people of equal status take turns to 'educate' each other? The term 'learning' is usually used for two people of equal status. So what exactly gives one the right to be an 'educator' instead of merely being a person another can 'learn from'?