Another aspect of professionalism might involve refraining from using the classroom as a place in which to "push" one's own personal agendas, especially one's political agendas. Students form in some ways a captive audience, and it is unfair to them to misuse one's authority to belittle and denigrate their political opinions unless one is fully prepared and willing to allow them to make their own arguments without making them feel intimidated. A truly professional teacher should be willing to tolerate and indeed even encourage disagreement with his/her own beliefs.
Another way of phrasing #7's comments would be to say that part of professionalism for a teacher is demonstrating what it means to be a life-long learner. We need to not only teach the children in our classrooms; we hope to instill in them, their families, and everyone with whom we have contact the importance and benefit of being open to continually adding to our base of knowledge, experience, and skills. In this position, we are not just teachers in the school building, but educators by example for the whole of society.
Professionalism to me means always being willing to reevaluate your practices when things don't go well. It also means being willing to learn from others. Of all the excellent teachers that I've seen over the years, the best shared a common trait: they always thought they could do better, and they always thought their colleagues, even first year colleagues, could teach them something worthwhile.
I think that professionalism to a teacher should extend beyond the classroom. Teachers are held to a higher standard than many other professionals. For example, look at the news stories which come out (horrifying to many good/great teachers). Teachers are under the scrutiny of the community at all times. While, for some, this may seem unfair, educators are responsible for molding the next generations. Therefore, teacher should take both their jobs and their own education very seriously.
There are so many different aspects to professionalism that we could discuss this all day. One aspect of professionalism to me relates to the kind of relationship that I form with my students. For me, it is important as a teacher to maintain some level of distance between myself and my students. This means practically that I don't try to be "just one of the gang" and I deliberately hold my self apart from students. I have often socialised with students, but only after I have finished teaching them. At the end of the day, my job as their teacher is to teach them, and having a friendship could interfere in that process. However, this is just one aspect of professionalism.
The above posts make excellent points. Professional educators, like professionals in any other career, need to be up to speed with current educational practices and to have a passion and knowledge for their subject area. As post 2 indicates, however, there is a responsibility to teach in the areas outside the boundaries of the curriculum. Educators need to show moral and social responsibility and accountability: I know some teachers rail against this level of responsibility, but our effects can be life-changing for our students. Most of us can recall the teacher who encouraged us, or the teacher who put us down. Professional educators have a tough job, but building people is a momentous task.
The first post pretty much has given an excellent summary of what it means to have professionalism as a teacher. To this answer, I would like to add two more points. Professionalism should also extend to interaction with colleagues. What can make teaching much better is to have peers that are good at what they do and act in a way that accords with their position as an educator. Second, professionalism should also extend to an individual's personal life as well to some extent. An educator is a high calling. So, there should be certain characteristics that are prized.
There are so many aspects of professionalism with regard to teaching.
There is professionalism in terms of being prepared in terms of the knowledge needed to teach in a given content area. A professional teacher has the knowledge that is required for any given lesson. If a teacher does not have that knowledge, he or she makes sure to obtain it before trying to teach the lesson.
There is professionalism in terms of being prepared from a pedagogical point of view. A professional teacher does not simply come into class hoping to "wing it." He or she must always plan lessons carefully and with some thought as to what to do in various situations that might arise within the lesson.
Finally, there is professionalism in terms of personal conduct. A professional teacher comes to work looking like a professional. Such a teacher also conducts him or herself in a manner that will communicate to the students that the teacher is serious about the job of educating them.