A three-phase study, with a different sample for each phase, involved a total of 1125 secondary school students in Indonesia. The first phase involving 373 grade 8 and 9 students was used to develop and validate an Indonesian classroom environment instrument with eight scales based on the Individualized Classroom Environment Questionnaire and the Classroom Environment Scale. In the second phase of the study, 502 Indonesian science students in grades 11 and 12 were involved in a translation, adaptation, and validation of a four-scale Indonesian version of the Test of Science-Related Attitudes. In the third phase, these new Indonesian attitude and environment scales were used with another sample of 250 Indonesian biology students in an investigation of the effects of classroom psychosocial environment on students' science-related attitudes. The finding of statistically significant associations between environment and attitudes replicated much prior work in science classrooms in developed countries. For example, more favorable science-related attitudes on several scales were found in classes perceived as having more personalization, participation, investigation, order, and organization. (Author)