Nationwide, many public school districts are struggling to keep arts education available for their students. One response to dwindling arts instruction has been the use of teaching artists. A teaching artist is at once a practicing artist and an educator. The formal empirical research on teaching artists is limited. This study used a mixed-method design, incorporating both surveys of and interviews with teaching artists, to develop a better understanding of the experiences and impact of teaching artists. A sequential quantitative-qualitative analysis process integrated two different data sets into a comprehensive whole that was able to suggest the beginnings of a stage theory of teaching artist professional development. Participating artists were from all four art areas (dance, music, theatre & visual arts) and had done teaching artist work in a k-12 public school. Teaching artists appear to begin at an improvisational stage when their approach to the work is spontaneous. Some move to a growth stage where they actively and enthusiastically explore and develop their teaching artist work. Lastly, there was evidence of an established stage where teaching artist work is focused and refined and artists were veteran practitioners of both art and teaching. Some artists, however, did not move through the stage theory but struggled with teaching work in a K-12 environment and were at the mismatched stage. There also appears to be two different orientations of teaching artists -- art-oriented and teaching-oriented. These findings have implications for schools and arts organizations in their use and preparation of teaching artists in public schools.