Numerous empirical findings have shown biased judgments of (future) teachers depending on students' ethnic and social background. Furthermore, research has indicated that (future) teachers' stereotypes and attitudes differ depending on students' backgrounds and appear to influence (future) teachers' judgments. Based on theories of stereotype change, attitude change, and judgment formation, a short intervention was developed to change stereotypes and attitudes and to reduce judgment biases. In an experimental study (within- and between-subject design) with N = 215 preservice teacher students, the effectiveness of the intervention on stereotype change, attitude change, and reduction of judgment distortions was tested. The results showed hypothesized effects of the intervention on stereotypes and attitudes towards students with an immigration background and students with low social status. Furthermore, the intervention showed effects on preservice teacher students' judgments, especially for low-status students.