The main reason for [teaching as a moral craft] is that, unlike most professionals, teachers do not apply their expertise toward ends that are set by the client. A lawyer, doctor, or accountant is a hired mind who helps clients pursue goals that they themselves establish, such as to gain a divorce, halt an infection, or minimize taxes. But teachers are in the business of instilling behaviors and skills and knowledge in students who do not ask for this intervention in their lives and who are considered too young to make that kind of choice anyway. By setting out to change people rather than to serve their wishes, teachers take on an enormous moral responsibility to make sure that they changes they introduce are truly in the best interest of the student and not merely a matter of individual whim or personal convenience. And this reponsibility is exacerbated by the fact that they student's presence in the teacher's classroom is compulsory. Not only are teachers imposing a particular curriculum on students, then, but they are also denying them the liberty to do something else. The moral implications are clear: If you are going to restrict student liberty, it has to be for very good reasons; you had better be able to show that the student ultimately benefits and that these benefits are large enough to justify the coercive means used to produce them (Cohen, 1988; Fenstermacher, 1990; Tom, 1984).
I've heard other people argue that the teaching profession doesn't compare well to other professions, like being a doctor or lawyer. After reading this, I'm happy they don't - teachers have good reason to feel like they're doing something special.
References
Labaree, D. F. (2003). The peculiar problems of preparing educational researchers. Educational Researcher, 32(4), 13-22. Retrieved from http://edr.sagepub.com/cgi/content/abstract/32/4/13.