This study explores the ways the leaders of three American congregations of women religious have prepared their sisters for the teaching apostolate both in the past and in the present. The study includes information on the founding of the communities, how their apostolates have evolved over time, factors that have contributed to the development of their programs of study in preparation for the apostolate, and the current experiences of sisters engaged in the teaching apostolate. Recent decades have seen research studies on sisters and their apostolic works from a historical or sociological perspective or examined past educational practices of particular religious communities or their colleges. The current study examines how sisters' studies have adapted over time to respond to various internal, external, and personal factors, and explores the contemporary experiences of women religious in the teaching apostolate. Site visits were conducted to each of the selected communities. Artifacts, observations, and interviews (one-on-one and focus groups) were the primary sources of data. Interviews were conducted with superiors or directors of studies, formation directors, archivists, and sisters who had entered their communities within the past 20 years and were currently engaged in teaching. Cross-case analysis of themes found that similar factors have influenced the evolution of the communities' apostolates and programs of study. The younger sisters engaged in teaching identified common difficulties encountered in teaching and common supports provided by their communities. Impacts of aging membership, fewer numbers of new vocations, and changing backgrounds and needs of new vocations surfaced in all of the cases and provided insight into present experiences of many religious congregations and the schools in which they serve. Since women who have entered these religious communities in recent decades have entered with academic degrees and in fewer numbers, adaptation and individualization, rather than standardization, best describe the programs of study. Historically, women religious were the primary source of staffing, leadership, and foundational vision that enabled the growth of elementary and secondary schools throughout the United States. While sisters today comprise a small portion of staff in Catholic schools, their influence, witness, and leadership continue. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]