Empirical Informal Teacher Leaders: Who They Are, What They Do, and How They Impact Teaching and Learning Stephen P. Gordon 1 , Jennifer Jacobs 2 , Susan M. Croteau 3 , and Rachel Solis 4 Abstract Educators in PK–12 schools were surveyed to seek their perceptions of colleagues who they considered informal teacher leaders, defined as leaders who were not appointed to a leadership role by a school or district administrator. The survey asked administrators, educational specialists, and teachers working in PK–12 schools across four states to share their perceptions of informal teacher leaders’ leadership activities, personal and professional attributes, relationships with other educators, and impact. Open, axial, and selective coding were used to analyze the respondents’ open-ended survey responses, and themes were developed relative to research topics. The respondents reported that the informal teacher leaders they identified engaged in important leadership activities at the individual, team, and school levels. The informal teacher leaders were described by respondents as passionate, caring, efficient, open to others, and professional. A variety of specific types of leadership knowledge and 1 Educational and Community Leadership Program, CLAS Department, Texas State University, San Marcos, TX, USA 2 Elementary Education, University of South Florida, Tampa, FL, USA 3 Texas State University, San Marcos, TX, USA 4 Rawson Saunders School, Austin, TX, USA Corresponding Author: Stephen P. Gordon, Educational and Community Leadership Program, CLAS Department, Texas State University, 601 University Dr., San Marcos, TX 78666, USA. Email: sg07@txstate.edu Journal of School Leadership 1-22 ª The Author(s) 2020 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/1052684620924468 journals.sagepub.com/home/jsl