This user's manual is intended to aid in the use of the Fourth Count (population) School District Data Tapes (SDDTs) derived from the 1970 Census. The manual, which is designed to complement the 1970 Census Users' Guide prepared by the United States Census Bureau, covers sources of the data, structure and contents of the tapes, and use of the tapes. Because school districts are not generally coterminous with area organizations used by the 1970 Census, school administrators could not apply the Census data directly. To alleviate this problem, the data tapes, which are a recompilation of the 1970 data, provide data tables for each school district in the country with 300 or more students. The tapes contain half of the data tables contained in the original census tapes, including all tables requested by several dozen educational planners consulted in the design phases of the tape development effort. There are 3,494 school district records in the data tapes, for an average of 2.5 school district records per high school. Data breakdowns include age, sex, Negro population, Spanish origin, mother tongue, place of birth, residence and housing arrangements, employment and occupational status, marital status, and economic status. An extract of these data tapes has also been prepared to supplement the main data files of the National Longitudinal Study (NLS) of the High School Class of 1972. The extract includes only those school districts that contained one or more high schools in the 1972 NLS sample. This manual describes the preparation of the SDDTs, tape labels and control information, record types, county components and administrative units, computer requirements, and tape format; and it provides code explanations and sample FORTRAN and COBOL access statements. (TJH)