Researchers generally credit Albert Bandura for providing the theoretical framework for studying collective teacher efficacy. Research shows that principals using transformational leadership behaviors significantly impact collective teacher efficacy. Policies, such as Every Student Succeeds Act, increasingly put pressure on school districts to improve student achievement or lose funding. Supporting literature and research shows that improving collective teacher efficacy improves student performance regardless of student socioeconomic status. Therefore, a department leader's ability to increase collective teacher efficacy amongst staff directly influences the student achievement within their school district. This researcher investigated the relationship between transformational leader behaviors of department leaders and collective teacher efficacy. The Multi-Factor Leadership Questionnaire, developed by Bass and Avolio and the Collective Teacher Efficacy Scale short form, developed by Goddard and Hoy were distributed in two counties in New York state to determine if a correlation existed between the perceived department leader's leadership style and the level of collective efficacy of the teacher. Evidence from the study indicates that transformational leadership behaviors and contingent reward behaviors associated with transactional leadership show statistical significance in improving collective teacher efficacy. This research will help school leaders and policymakers better expend resources fostering collective teacher efficacy. Lastly, it demonstrated the importance of department leaders and leadership behaviors that improve collective teacher efficacy, thereby improving student achievement. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]