Focusing on the acquisition of science processes, a study was made of the relationship of acculturation and social class to cognitive development among 1,677 lower and lower middle class students enrolled in the public high schools of three rural, 11 semi-urban, and three urban communities. Acculturation was defined at the community level in terms of formal education, wage employment, and urbanization. Social class was defined at the individual level in terms of father's level of formal schooling, occupational prestige, and income. As groups, students in classrooms were administered tests for about 3 hours. Measures included a standardized nonverbal intelligence scale; a group embedded-figures test; a test of the ability to make generalizations; group conservation tasks; and a test of ability to perform basic science processes of observing, comparing, classifying, quantifying, measuring, predicting, inferring, and experimenting. Three scales were developed and administered; these concerned life processes/cycles of animal and plant life, inferential reasoning about internal states of others, and natural phenomena. In addition, questionnaires on family characteristics were completed by students and parents. Among the findings was the observation that nonverbal reasoning, abstract reasoning, higher levels of development, and better understanding of science processes appear to be enhanced by more years in secondary school, membership in a social class above the subsistence level, and living in a more acculturated environment. (RH)