Coming from an artistic background (undergrad degree from SCAD), I have been firmly in the “art” camp on this topic in the past, though the more time I spend in school, the more I appreciate the “science” perspective. Teaching is an art much as doctoring is an art - every new teaching experience with a particular student or group must be addressed as a unique situation that has never happened before. Science can give us clues as to what is more likely to work in the new situation, but we cannot be certain our strategies will work in the same way every time.
Two things in particular make teaching an art: (1) understanding the evolving, situational reality of the classroom and (2) figuring out and implementing the best course of action to take in each experience. Webster's dictionary gives several definitions of art that can be used to support the idea of teaching as an art: (1) “the activity of using imagination and skill to create beautiful things”, (2) “a field or category of artistic activity”, (3) “a trade or craft and the methods employed in it”. I take these definitions to imply that teaching as an art involves both imagination and skill to reach the desired outcome, usually student learning (a process, not a product), and that teachers hone their craft over time.
To these concepts I would suggest we add intuition, as most of the work involved in the maintenance of the proper social-emotional classroom climate for learning is done on-the-fly and moment-to-moment as an extreme form of multi-tasking. Webster's dictionary defines science as (1) “the study and theoretical explanation of natural phenomena”, (2) “a systematic activity requiring study and method”, and (3) “knowledge, especially that acquired through experience”. Most teaching is systematic and requires intensive study before entering the profession and throughout an educator’s career. The accumulation of information and enhancement of teaching practices based on feedback suggests a science of teaching. However, the most effective teachers are an expert in both teaching methods (art) and subject matter (science).
To become a maser educator is to integrate both elements of teaching through the application of feedback gained through action research occurring within the context of the situational nature of the classroom. Educators who reach this point in their profession appreciate the interrelated and synergistic combination of artistic and scientific elements in teaching. In short, I believe it is the application of the science that constitutes the art.