Research Findings: Recent research has explored relations between classroom quality and child executive function (EF), but little is known about how teachers' well-being, including stress, relates to child EF--a crucial component of self-regulation. We hypothesized that teacher stress is negatively or curvilinearly related to child EF and classroom quality may be one mechanism explaining this relation. Furthermore, as working with young, low-income children may be particularly stressful, we tested the extent to which the relation between teacher stress and child EF varies by school-level poverty. Two-level hierarchical linear models using a sample of 171 kindergarten children and 33 teachers revealed a marginally significant linear relation between teacher stress and child EF (spring) controlling for baseline child EF (fall); there was no evidence for mediation by classroom quality. School-level poverty moderated the relation between teacher stress and child EF: Children attending low-poverty schools demonstrated smaller gains in EF when their teachers reported higher stress levels. However, in high-poverty schools high levels of teacher stress were not a risk factor for child EF. Practice or Policy: These novel findings are a first step to understanding how teachers' well-being relates to child EF across schools and have implications for supporting teachers.