The assistant principal position is a middle management position that can be challenging and lead to burnout, attrition, and turnover. There is little research on the characteristics of the assistant principal position, the impact of policy, and the role that positive psychological resources play in explaining well-being. With a sample of 184 public school assistant principals in Texas, this mediation study tested the relationship between their socio-cognitive mindfulness, psychological capital, perceived supervisor support, and thriving. Findings indicated that assistant principals' socio-cognitive mindfulness, psychological capital, and perceived supervisor support significantly correlated with thriving. Multiple linear regression revealed that psychological capital and perceived supervisor support predicted thriving. Also, psychological capital fully mediated the relationship between socio-cognitive mindfulness and thriving, but perceived supervisor support did not mediate that relationship. The findings prove the importance of placing early career assistant principals with highly supportive supervisors. Districts can consider providing training and professional development to increase sociocognitive mindfulness and psychological capital to enhance assistant principals' well-being. [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.]