The National Education Longitudinal Studies (NELS) program is a long-term effort that now encompasses the educational experience of youth from three decades, the 1970s, 1980s, and 1990s. The NELS program studies the educational, vocational, and personal development of students at various grade levels, and the personal, familial, social, institutional, and cultural factors that may affect that development. The NELS program currently consists of three major studies: (1) the National Longitudinal Study of the High School Class of 1972 (NLS-72); (2) High School and Beyond (HS&B); and (3) the National Education Longitudinal Study of 1988 (NELS:88). This monograph discusses opportunities for drawing comparisons across the cohorts that comprise the three studies, as well as some of the differences in survey content and design that may limit the possibilities of drawing valid comparisons. The focus is on high school transcripts. When transcript information is coupled with other data about students, it permits the specification of complex models of educational processes and the measurement of high school program and course effects on post-high school outcomes. Comparison of transcript information among the three studies means attention to issues of content comparability and sample design. Content comparability is discussed in the "crosswalks" that form the final section of this report, and design comparability is discussed in some detail. Some other difference of note among the studies are discussed, but their general designs were quite similar. The attached crosswalks cover student-level and course-level comparisons. (Contains 4 tables and 19 references.) (SLD)