This qualitative phenomenological interview study examined the experiences of principals who completed Stanford University d.school's School Retool fellowship program for school leaders, which focused on using the design thinking process for school improvement toward deeper learning. This research project explored the leadership practices and tools used by principals toward deeper learning. To better understand this phenomenon, the "Coherence Framework" (Fullan & Quinn, 2015), which includes the elements of focusing direction, cultivating collaborative cultures, deepening learning, and securing accountability, was used to frame the study and analyze the findings. This study addressed the following research questions: a) How do pre-K-12 principals use design thinking for school improvement and b) How, if at all, do principals see design thinking practices as a tool that can impact deeper learning of students from different backgrounds? Thirteen principals from across the United States were selected for this study. Virtual semi-structured interviews were conducted as the primary data source. Findings indicated a strong relationship between the beliefs and practices used by principals when implementing design thinking, making it difficult to disentangle the findings and emergent themes between the two research questions. Overall findings of the study suggested: principals' leadership styles, takeaways from professional learning, and beliefs influence how they view and utilize the design thinking approach; principals use design thinking tools, artifacts, and mindsets for school improvement; participants worked to foster collaborative communities; and principals attempted to use empathy to build equitable practice. This study provided evidence that principals can use design thinking tools and practices for school improvement toward deeper learning, using the resources that schools already have. Implications from this study suggested that principals play a significant role in fostering collaboration within the school community through learning leadership and that principals facilitate professional learning around design thinking in different ways, including through formal and informal structures such as scheduling and supervisory practices, hiring practices, and the mindsets that they modeled. Like principals, school district leaders can influence ow people engage with design thinking through the professional learning they facilitate and/or support, as well as the formal and informal structures that they put into place. This study suggests that School Retool directors and local collaboratives additional explicit instruction related to building equity is needed for principals. Recommendations for policy and practice are addressed and highlight the need for principals to have clearly defined visions related to student learning goals prior to implementing design thinking. Additionally, it is recommended that principals complete training with a faculty member to increase buy-in and that principals utilize an enhanced version of the design thinking process to build equitable practices within their schools to support students from different backgrounds. It is recommended that state policymakers fund research on different types of professional learning for school leaders, such as design thinking, which focuses on student outcome data. Recommendations for future research address and highlight the need for additional studies to identify findings related to principal practices, teacher practices, and student outcomes. [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.]