Teacher retention is a challenge for schools across the country. For private and independent schools, teacher attrition is twice that of public and charter schools. The rate of teacher attrition has increased dramatically attributable to the global pandemic, making this a critical issue for K-12 education. Using an Improvement Science approach, this mixed methods research study examined teacher departures at the Essex School, a pseudonym, a small independent school in the Northeast U.S. which saw teacher attrition escalate to 26.6% for the 2019-2020 school year. Three primary drivers were identified: 1) teacher collaboration, 2) teacher leadership, and 3) school culture. Three change ideas were implemented: 1) a teacher leadership committee; 2) structured administrative support to encourage teacher collaboration; and 3) teacher thought partnerships. Overlapping PDSA cycles gathered data from teacher surveys, reflective journals, and focus groups. The lagging measure of teacher retention was measured by contract renewals. Three master themes emerged that support teacher retention: 1) leadership and professional value, 2) collaboration and professional relationships, and 3) perceptions of school culture. Teacher leaders stepped confidently into leadership and exhibited strong ownership of study outcomes. Teacher collaboration increased when supported in meaningful ways by the administration. The combination of leadership and collaboration increased teacher commitment to and engagement in the school. Teacher retention for the teachers participating in the study (87.5%) was significantly higher than for the general population of teachers (67.2%). [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.]