'Are principals instructional leaders yet?' A science map of the knowledge base on instructional leadership, 1940–2018

In the 1980s when research on effective schools surfaced the importance of ‘instructional leadership’ in the United States, skeptics wondered if this would be just another educational fad. Yet, 40 years later, the expectation for school principals to be ‘instructional leaders’ has become ubiquitous throughout much of the world. This systematic review of research used science mapping to gain insights into the growth and geographic distribution of this literature, as well as to identify key documents, authors, and topics. The authors used a variety of quantitative bibliometric analyses to examine 1206 Scopus-indexed journal articles on instructional leadership published between 1940 and 2018. The results affirm that the knowledge base on instructional leadership has not only increased in size, but also geographic scope. Contrary to expectations during the 1980s, instructional leadership has demonstrated remarkable staying power, growing into one of the most powerful models guiding research, policy and practice in school leadership. Despite this finding, both author co-citation and co-word analyses revealed the emergence of ‘integrated models of school leadership’ in which instructional leadership is enacted in concert with dimensions drawn from complementary leadership approaches. Key themes in the recent literature include studies of leadership effects on teachers and students, contexts for leadership practice, and means of developing instructional leaders.