This study investigated characteristics and behaviors of middle school principals that enhance the efficacy of new and experienced middle school teachers. Existing research has established a positive relationship between high levels of teacher efficacy and increased student achievement. Prior research has also demonstrated a positive link between principal behavior and the efficacy of teachers. In this study, a diverse group of middle school teachers from a mid-Atlantic state were surveyed using the Teacher Sense of Efficacy Scale along with a researcher-developed Likert-type scale asking participants to rate research-based principal behaviors. In addition, responses to demographic questions were obtained to compare principal behaviors and teacher efficacy across the domains of gender, poverty level of school, size of school, and school location (urban, suburban, rural). Responses from 366 teachers were analyzed using stepwise multiple linear regression to determine whether various principal behaviors affected new and experienced teachers differently. Findings suggest that teacher efficacy is significantly affected by principal behaviors based on years of teaching experience. Whereas newer teachers required more support and modeling from their principals, the efficacy of more experienced teachers was influenced by emotional factors such as inspiration and purpose. Statistically significant findings were obtained in each of the demographic comparisons as well. These findings may inform principals and principal trainers of best practices in enhancing teacher efficacy, thus supporting increased student achievement. The provision of additional support and supervision based on the needs of teachers can also be addressed by using the results of this study. Implications for teacher retention and principal training are discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]