This report examines the demographic trends, social realities, and complexities that can potentially transform American secondary schools. It describes the nature of diversity in the world and nation and between and within states and school districts. Such information can be useful in selecting successful strategies for implementing changes in the country's diverse secondary schools. The report includes: "Introduction" (Gerald N. Tirozzi); "The World's Population: The Next 100 Years" (who will care for us when we are old, rich and poor people and nations, and the role of corporations and nations); "The U.S. Population as Part of the World's Six Billion People" (e.g., minorities and majorities, diversity, the baby boom ages, the blurring of racial identity, economic desegregation, race and national origin, the increasing number of elderly, leading a school full of strangers, metropolitan areas, and rural schools); "Schools and Principals in a Changing Social Context" (principals and schools, the issue of paid non-teaching staff, and principal problems); "Specific School-Site Issues Facing Principals" (e.g., where enrollment increases will occur in the future, whether the Internet holds promise for reducing the number of high schools, and how curriculum and school governance will change); and "Conclusions" (diversity in the world and in the United States, principals and diversity, and recommendations). (Contains 14 references.) (SM)