Educational and vocational plans and changing characteristics of Indiana high school seniors from 1966 to 1980 were studied. In 1966, 1969, 1972, and 1975, questionnaires were mailed to all public and private high schools in the state, while in 1980, a stratefied random sample was used. The response rate of the first four surveys was 54 percent or higher: there were 37,800 high school seniors in the class of 1966, 46,500 in 1969, more than 51,500 in 1972, about 50,000 in 1975, and nearly 12,000 in 1980. Overall (total) data for all five classes are presented on: characteristics of high school seniors, including sex, race, course concentration, grade average, and size of community; and characteristics of the head of household, including highest educational level attained. The plans of high school seniors who plan to continue their education (college choice, field of study, financial arrangements, and school location) are addressed, and comparisons are made between classes. Information is also presented on seniors who plan to delay the continuation of their education for six months or longer after high school graduation, as well as on those who do not plan to enroll in an educational program in the future. In addition to considering seniors' characteristics and plans for each of the five classes, interrelationships of student characteristics and plans by ethnic background and sex are examined for the class of 1980. Appended materials include a sample questionnaire and a list of educational and training programs by degree level. (SW)