Time is the most valuable currency in schools. This study describes how successful high school principals reported spending and allocating their time to various leadership tasks using selected items from a study of principal-time use and school effectiveness in Miami-Dade County Public Schools in Florida US. Public high school principals were selected based on their 2019 Missouri School Improvement Program performance indicators and asked to complete either a paper or online survey. Findings show that principals spend more time on management-related activities than curriculum and instruction-related activities. There is a strong association between time-use on curriculum and instruction with both gender and school size. The more leadership experience a principal has, the less time they are likely to spend on school management activities. Time-use on organization management is strongly associated with school size. If instructional leadership is a fundamental priority for principals, then development and support of successful principalship will require a redesign of their roles to free time for instructional leadership. School districts that hire principals from a pool of assistant principals (AP) or invest in principal pipelines, need to develop a strategy to build APs’ instructional and leadership skills. Keywords : High school principals, principals’ time-use, principals’ roles, successful principals, instructional leadership. DOI: 10.7176/JEP/11-18-01 Publication date: June 30th 2020