Among all in-school factors that impact student learning, teachers carry the most weight -- but school leaders are not far behind. Decades of research have proven the positive influence principals can have on student achievement, school climate and teaching quality. New evidence suggests that their impact may be even greater than previously thought, as principals continue to assume the roles of instructional and change leaders. This new Policy Snapshot identifies two major themes in state legislation introduced between 2017 and 2020 concerning the development of, and support for, school leaders: (1) Pre-service training and induction programs?that prepare leaders for the job; and (2) In-service professional development training?that supports student needs and success. This resource builds on a similar Policy Snapshot, published in 2019. [For "School and District Leadership. Policy Snapshot," see ED603064.]