This brief uses national data from the High School Longitudinal Study of 2009 to investigate deficit beliefs, or beliefs that students' academic underperformance is primarily attributable to deficiencies in their home environments, among high school math teachers. Descriptive results reveal that students in low-level math courses have teachers with more deficit beliefs. Regression results show that net of extensive control variables for both student and teacher characteristics, having a math teacher with stronger deficit beliefs is significantly and negatively associated with students' math performance. However, this negative association is not more pronounced for youth from minoritized and low socioeconomic status backgrounds.