Mastery motivation is considered important because it promotes competence and is believed to be the precursor to achievement motivation. Focusing on toddlers between 16 and 22 months old, this study examined the relationship between mastery motivation and environmental contributors, such as maternal expectations, and cultural orientation in Puerto Rican and Dominican mothers. The study's goal was to determine how factors in the socializing environment contribute to children's mastery motivation. Participating were 46 mother-child dyads in Bronx, New York: 35 Puerto Rican and 12 Dominican dyads. Mothers ranged in age from 17 to 44; the majority were born in the United States; mothers had an average education level of 12 years, and an average of 2.53 children in the families. Mastery motivation behaviors were assessed using the Individualized Assessment for Mastery Motivation and the Dimensions of Mastery Questionnaire. Mothers also completed questionnaires assessing their child's development, their expectations, their attitudes regarding individualism-collectivism to assess their cultural orientation, and other aspects of family life. Findings indicated that the children exhibited levels of object-oriented persistence comparable to those in past research. The Puerto Rican mothers appeared to value and encourage their children more highly in the social than the object domain. Very few relationships between object-oriented mastery motivation variables and maternal characteristics and expectations were confirmed for the sample as a whole. The difference in findings obtained for the two groups suggests that Latino groups should be examined separately. (Contains 34 references.) (KB)