Although the roles of instructional leader and lead learner have become central in the work of 21^st century principals, their professional development has garnered little attention. This quantitative, non-experimental, comparative survey study investigated differences in the self-reported leadership behaviors of principals who identified themselves as using either supported or unsupported professional development. Brain based learning, constructivist learning, and adult learning theories, together with professional development standards, created the conceptual framework for this study. Participants were obtained through a purposive national sampling of 7,000 of 230,600 U.S. principals, delimited to leaders in their school for 2 years or more. The voluntary, anonymous online survey yielded 186 usable surveys. The Principals Instructional Management Rating Scale was used to measure leadership behaviors. The t-test of means was used to compare the means of responses from supported and unsupported principals for each leadership domain. Supported principals' means of responses were higher for Domain 1 (defining the school's mission). The difference in means, however was not statistically significant when subjected to the Bonferroni correction adjustment for potential family wise errors. Research suggests the strongest link between student achievement and leadership practices is Domain 1 leadership behaviors, thus warranting further investigation of the use of principals' professional learning communities and trained mentors/coaches. Implications for positive social change include further understanding of the importance of high quality professional development for school leaders to support their work in defining the school's mission.