Teachers should constantly ask themselves this question, especially those who seek to develop professionally. Often, those who stop asking themselves if they are good teachers, think that they have reached the "top" and that there is nothing new that they can learn or contribute to their career. They are, I believe, wrong!
We can analyze this question semantically or pragmatically. Semantically, the question "Am I a Good Teacher?" is explicit: A teacher who asks himself/herself this question usually wants an answer, yes or no. In other words, he/she is earnestly asking himself if he/she is good. But pragmatically, the question can lead to an in- depth interpretation. It is not a question, but it is a "speech act" that cannot be measured by its truth value. We call this type of question 'self reflection' in which a teacher is likely searching for ways to improve herself/himself professionally, to make changes that will lead to better results for her students.
We can assume that the a teacher would ask himself/herself this question if he/she believes that he/she is not a good teacher and he/she needs some advice to make changes in his/her teaching. He/ she might turn to his colleagues or students.
But, he/she could also follow the following steps:
First, he/she could observe himself/herself and reflect on his/her observations.
One way to do this is to record one or more of his lessons, and later review them, or even ask a trusted colleague to listen to the recordings and give him/her some feedback.
Next, he/she might also ask some colleague to observe his/her classes and reflect on his/her observations. However, the teacher should be open-minded and ready to accept feedback, and even criticism.
Another excellent course would be to ask another colleague's permission to observe her lessons, perhaps for a period of time. A teacher who seeks to improve is likely to learn from observing other teachers, and this often leads to a great deal of reflection about one's own teaching.
A direct and interesting way to answer this question "Am I a good teacher", is to ask the students to reflect on how you teach. This can be done by asking questions, at the end of each class, such as do you enjoy the lesson? Do you think the teaching instruction suites the topic discussed? What can be done to enhance your comprehension?
The teachers may also use an evaluation form to be filled anonymously by the students at the last minutes of the lesson, and later the teachers could analyze these forms and draw inferences. This activity may strengthen the relationship between the teachers and students. Teachers should avoid asking the students questions relating to the teacher's personality and appearance.
I believe that asking yourself if you are a good teacher is essential for being a good teacher, and will lead to improving the way that you teach, while preserving the strong aspects of your teaching. Teachers should be honest with themselves when answering this question-- otherwise they should perhaps look for a profession rather than teaching.
For further reading:
Crookes, G. (2003). A Practicum in TESOL: Professional Development through Teaching Practice. Cambridge University Press.
Naik, S. P. (2004). Theory of Teacher Training. Anmol Publications PVT. LTD.
Oxford, R. L. (1990). Language Learning Strategies. Heiele and Heinele Publishers.
Richards, J. C. and Nunan, D. (1990). Second Language Teacher Education. Cambridge: Cambridge University Press.
Wallace, M. J. (1991). Training Foreign Language Teachers. Cambridge: Cambridge University Press.