To examine whether developmental changes occurred and whether motivation to maintain good health was related to sex and socioeconomic status, a longitudinal study of third and seventh graders was conducted at five semiannual intervals. Data were obtained from subjects' responses to the Mouth-Appearance Pictures, a group-administered forced-choice task consisting of a set of nine pairs of pictures which require a child to choose between a more attractive but less healthy mouth and a less attractive but more healthy mouth. Of the 1,341 respondents who participated in the first questionnaire administration, 605 completed all five sessions. Health motivation was found to decrease linearly with age and to be inversely related to socioeconomic status in the younger sample. Implications for health education programs, theory, and future research are discussed. (Author/RH)