It is important for teachers to be able to accurately assess students' performance. Such judgments can be influenced by characteristics of the student Südkamp et al. (J Educ Psychol 104:743-762, 2012. 10.1037/a0027627). Besides students' actual performance, students' group characteristics (e.g., gender or immigration background) may effect teachers' judgments. In addition, judgment accuracy might be different for various student groups. We conducted an online study of 168 preservice teachers. We presented within a virtual classroom mathematics test results of 12 fictitious second-grade students who differed in their actual performance in a mathematical test, immigration background, and gender. Preservice teachers made a judgment about the students' current performance. Students' actual performance, immigration background, and gender showed statistically significant main effects on the "judgment." Students with (vs. without) an immigration background and female (vs. male) students were evaluated less favorably. These effects were qualified by a statistically significant three-way interaction between actual performance, immigration background, and gender. The joint examination of student characteristics in terms of "judgment accuracy" shows that it is precisely the interaction of student characteristics that makes a difference: female students with and without an immigration background as well as students without an immigration background are assessed more accurately, while male students with an immigration background are assessed significantly more inaccurately. In sum, the judgment made by preservice teachers about students' performance differed in terms of student characteristics that were unrelated to performance such as immigration background and gender in addition to differing on performance-related variables.