Using integrated threat theory as a theoretical framework, this multiple case study analyzed the effects of threat and the perception of threat from immigrants on the attitudes of teachers toward their elementary school students. The study was conducted with teachers at five northern California schools. All of the teachers were experienced and well-trained, teaching in low-income neighborhoods with large immigrant populations. In support of integrated threat theory’s premise, results indicated that where threat was present or perceived, teachers’ words and reported teaching behavior indicated prejudicial attitudes toward students. The lack of threat corresponded to a lack of bias. It was found that teaching behavior that reflected prejudicial attitudes affected a number of areas of instruction. Specifically, teachers spent less time in informal interaction with students, limiting their familiarity with the children. Curricular decisions were affected in subtle ways, and there were examples of implicit bias in interaction. The report concludes with recommendations for practice and further research. Recommendations for policy are particularly important, as teacher education programs and school districts are both able to provide anti-bias training.