This research focuses on understanding how emergent pragmatic teacher-leaders impact institutional and organizational effectiveness in the absence of consistent school administrative leaders at an urban high school. In this mixed-methods case study, the author investigated the process of cultivating informal authority, the benefit of practicing social-emotional competencies skills, the strategy of managing staff resistance, and the roots of staff stability. The data sources included an online survey, individual interviews, and supplemental memos. Forty-three participants completed a questionnaire about their perceptions of leadership skills. Four participants completed a semi-structured interview about their understanding of formal and informal authority as well as institutional and organizational effectiveness. This research concludes: (a) Black or African American teachers are most likely to exhibit leadership qualities in the Emergent Pragmatic Teacher Leadership model concerning Administrator-Teacher Relationship. (b) Indicators Trust and Emotional Intelligence as well as Staff Relationships both contributed to Institutional and Organizational Effectiveness. (c) Emergent Pragmatic Teacher Leadership arises with a certain level of informal authority during turbulent school administrative leadership to maintain consistent expectations and continuously improve best practices. (d) These Emergent Pragmatic Teacher-Leaders embrace their professional core values to mitigate conflicts and staff resistance. Lastly, (e) in the absence of consistent administrative leadership, returning teachers create efficacious support networks and take ownership of their work despite there being many reasons to leave the profession. The author concluded this paper with the limitations of sample size and implications of the findings and potential future researches. This study may help urban schools and districts improve institutional and organizational effectiveness concerning school stability and staff collegiality so that teacher-leaders, school administrative leaders, district administrative leaders, and other stakeholders can collectively build sustainable work environments for the betterment of students. [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.]