Detailed instructions on what should and should not be counted as regular schooling (which were not routinely shared with respondents) were included in the Manual for 1982 forward. In its definition of "regular school," the Manual directed, "For this question include regular schooling in graded public, private, or parochial schools, or in colleges, universities, or professional schools, whether day school or night school. Regular schooling is that which advances a person toward an elementary or high school diploma, or a college, university, or professional school degree. Count schooling in other than regular schools only if the credits obtained are acceptable in the regular school system."

Persons who passed a high school equivalency test (i.e., the GED) or finished high school in the armed forces were coded as completing 12 years. For persons who completed more than 4 years of college, or who attended professional (e.g., law, medical, dental) school after completing 4 years of college, the responses are coded as 17+ years completed.

The Manual specified a wide range of training and educational activities which should not count as "regular schooling" when reporting highest grade/year of schooling completed. This included the following: 1) education obtained at vocational schools, business schools or colleges, and other trade and specialized schools unless such schools are part of a regular school system; 2) training received by mail from "correspondence" schools, unless the correspondence course counted toward promotion in a regular school; 3) any kind of "on-the-job" training; 4) adult education classes, unless such schooling is being counted for credit in a regular school system and advances the person toward an elementary school certificate, high school diploma, or college degree; 5) any type of basic military training; and 6) training under the Comprehensive Employment and Training Act (CETA) or the Job Training Partnership Act (JTPA), unless such training was given for credit at a regular school.

The Manual also instructed interviewers on how to code years of schooling from "miscellaneous school systems," including foreign schools, ungraded schools, night schools, instruction by tutors, schools graded by levels of "readers," "normal" schools, and special schools for the handicapped. In each case, the interviewer was to "enter the equivalent grade in the regular American school system."

For 1969-1981, information on the highest grade of schooling completed was collected for persons age 17 and older; beginning in 1982, such information was collected for persons age 5 and older. This change in universe obviously increased the proportion of cases reporting less than 12 grades of school completed.