An investigation of third- through ninth-graders' health-related cognitions used a health belief model to elicit perceptions of vulnerability to health problems, health benefits accruing to health actions, intentions of taking health actions, preventive attitudes, health motivation, beliefs about toothbrushing frequency, and selected beliefs about teeth. Data were obtained from a group-administered questionnaire including forced-choice, expectancy, and semantic-differential formats. Multiple analysis of variance indicated that health motivation decreased appreciably and in linear fashion with age and that perceived vulnerability was nonlinearly and complexly related to age. Most health-related cognitions remained largely stable and did not change appreciably during childhood or adolescence. Gender had some effect, particularly upon perceived vulnerability. Socioeconomic level had few clearcut and consistent effects. This report details study methodology and procedures, results in each of the categories, and implications including the need for health educators to re-examine their assumptions about socioeconomic, sex, and age effects of students' health attitudes and behaviors. (CB)