Are motivated students less likely to express negative achievement emotions in math, and how do teachers impact such academic beliefs? Guided by the situated expectancy-value theory and the control-value theory, this study is interested in how teacher support influences students’ negative affect in math through students’ perception of teacher support and students’ interest value (teacher-to-student transmission between and within classes). Thus, associations were modeled at the individual and classroom levels to investigate cross-level interactions. Using data from 1,429 students in grades 7–12 (49% males, 67% Hispanic Americans, 15% Asian Americans, 18% other racial/ethnic groups), cross-level indirect effects suggested an association of teacher-reported support for collaboration and cognitive support with decreasing negative affect through students’ perception of teacher support and students’ interest value. These associations were supported within but not between classes.