Teacher turnover continues to be a chronic problem for low-income schools and is especially high in urban charter schools. New evidence shows that teachers' perceptions of school leadership and trust are two of the most powerful predictors of turnover. Using interviews with former No Excuses charter school (NECS) teachers, this study seeks to better explain the mechanisms influencing teacher turnover by analyzing teachers' perceptions of what principals do to influence relational trust and describing how this influences teachers' decisions to leave. Findings show how high and often-implicit expectations principals have for teachers affect teacher-principal trust relationships in ways that lead to turnover.