Friendships provide opportunities to build empathy and practice social skills. Being friends with ethnically diverse peers can create opportunities for academic and social learning different from the opportunities afforded by same-ethnic friendships. Through my observation, I had been finding that elementary and secondary school students are less likely to have friends of a different ethnic — even from the beginning to the end of a single school year, as they progress in school. My observation show that most childhood friendships are formed in classrooms, but children tend to form friendships with others of their own ethnicity, with interethnic friendships decreasing across ages and grades. The observation looked at student and classroom factors that affect the likelihood of children forming friendships across ethnic. On an individual or student level, I looked at age, ethnic, and psychosocial factors, including sociability, internalizing behavior (such as worrying or feeling sad) and externalizing behavior (such as acting out or getting in trouble). I also examined factors related to classroom context, including teacher support, whether teachers treat students with varying levels of academic achievement differently, and competition among students. Results suggest that same-ethnic friendships increase over the school year, with greater increases among white and older children. Externalizing behavior predicted a greater increase in same-ethnic friendships, particularly among ‘domestic’ (Javanese: ‘cah kene dewe’) students. Teachers and classroom context influenced student friendships in two different ways. It suggests that teachers may make a difference in how students select and maintain friends. Classroom support -- measured by student perceptions of teachers' warmth, respect, and trust -- predicted less of an increase in same-ethnic friendships from fall to spring. In last, my observation points to the need not just for diverse schools, but also for teachers to foster classrooms where students and teachers support one another, and social and academic hierarchies are not dominant, which could increase the likelihood of students developing and maintaining interethnic friendships.