Equitable assessment of students' mathematical thinking is imperative for effective instruction. This two-part study investigated teachers' judgement of students' mathematical thinking. In Study One, we used a national data set to determine the correlation between teachers' judgement of students' mathematical thinking and scores from a standardised measure of mathematics. The relationship was further explored to determine whether teachers' perceptions of student-teacher conflict influenced their judgments about students' mathematical thinking. Results demonstrate that teachers' ratings of mathematics thinking significantly predicted students' standardised scores. Results indicate that teachers' perceptions of student-teacher conflict also moderated this relationship. Specifically, teachers' judgments have a higher correlation with students' standardised scores when conflict is high. In Study Two, the exploration is deepened by asking practicing teachers to evaluate a fictional classroom scenario.