In this investigation, methodological and substantive issues regarding early mastery motivation (also termed competence motivation and effectance motivation) were examined longitudinally using a primarily middle-class sample of 37 children observed at 1 and 3.5 years of age. Data on cognitive competence and mastery motivation were collected in order to accomplish (1) a psychometric evaluation of the instruments used to assess mastery motivation; (2) an exploration of the interrelations between cognitive competence and motivational functioning; and (3) an examination of the continuity of these relationships over time. Measures at 1 year of age included play assessments focusing on exploratory behavior in free play, executive functioning in elicited play, and cognitive competence. At follow-up assessments when the subjects were older, observations were made of children's spontaneous exploration of the Banta Curiosity Box; cognitive competence was again assessed. Standardized measures of cognitive competence included, at time 1, The Bayley Scales and, at time 2, The McCarthy Scales. Results, which indicated continuity in child functioning between 1 and 3.5 years of age, are discussed. (RH)