This study explored the relationship between principal leadership style and collective teacher efficacy in K-12 schools across five districts in South Carolina. The research problem addressed how different leadership styles--transformational, transactional, and passive-avoidant--affect teachers' collective beliefs in their ability to positively influence student outcomes. A correlational quantitative research design was employed to examine the relationship between leadership style and collective teacher efficacy. The guiding theoretical framework was based on transformational leadership theory. Data was collected using the Multifactor Leadership Questionnaire. Descriptive statistics, Pearson's correlation, and one-way ANOVA were used to analyze the data and answer the research questions. The findings revealed a statistically significant positive correlation between transformational leadership and collective teacher efficacy. Conversely, a statistically significant negative correlation was found between passive-avoidant leadership and collective teacher efficacy. No significant correlation was identified between transactional leadership and collective teacher efficacy. The one-way ANOVA results indicated significant differences in collective efficacy levels based on leadership style, with transformational leadership associated with the highest levels. The study concluded that principal leadership style plays a vital role in shaping collective teacher efficacy. It recommends that educational leadership programs emphasize transformational practices. Future research should explore other factors influencing teacher efficacy and further investigate the impact of transactional leadership in educational settings. [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/en-US/products/dissertations/individuals.shtml.]