Report amended November 1, 2018. Has the elementary and secondary teaching force changed in recent years? And, if so, how? Have the types and kinds of individuals going into teaching changed? Have the demographic characteristics of those working in classrooms altered? This report summarizes the results of an exploratory research project that investigated what trends and changes have, or have not, occurred in the teaching force over the past three decades. Our main data source was the Schools and Staffing Survey (SASS) and its supplement, the Teacher Follow-Up Survey (TFS) – collectively the largest and most comprehensive source of data on teachers available. SASS/TFS are collected by the National Center for Education Statistics (NCES), the statistical arm of the U.S. Department of Education. We took advantage of both the depth and duration of these data to explore what changes have taken place in the teaching force and teaching occupation over the three decades from 1987 to 2016. The results show that the teaching force has been, and is, greatly changing; yet, even the most dramatic trends appear to have been little noticed by researchers, policy makers, and the public. The report summarizes seven of the most prominent trends and changes; we found that teaching force to be: Larger Grayer Greener More Female More Diverse, by Race-Ethnicity Consistent in Academic Ability Unstable For each of the trends, we explore two large questions: 1. Why? What are the reasons for and sources of the trend? 2. So what? What difference does it make? What are the implications and consequences of the trend?