Teachers play a critical role in the success of their students, both academically and in regard to long term outcomes such as higher education participation and economic attainment. Expectations for teachers are increasing due to changing learning standards and a rapidly diversifying student population. At the same time, there are perceptions that the teaching workforce may be shifting toward a younger and less experienced demographic. These actual and perceived changes raise important questions about the ways teacher education may need to evolve in order to ensure that educators are able to meet the needs of students and provide them with classroom experiences that will put them on the path to future success. "Changing Expectations for the K-12 Teacher Workforce: Policies, Preservice Education, Professional Development, and the Workplace" explores the impact of the changing landscape of K-12 education and the potential for expansion of effective models, programs, and practices for teacher education. This report explores factors that contribute to understanding the current teacher workforce, changing expectations for teaching and learning, trends and developments in the teacher labor market, preservice teacher education, and opportunities for learning in the workplace and in-service professional development. [Contributors include Committee on Understanding the Changing Structure of the K 12 Teacher Workforce; Board on Higher Education and Workforce; Policy and Global Affairs; Board on Science Education; and Division of Behavioral and Social Sciences and Education.]