What are the boundaries for teachers' freedom of expression in public, secular schools in Canada? Drawing from the constitutional text, legislation, and normative expectations emerging from the literature, this article examines the scope given to teachers' expression in landmark case law. The analysis shows that the binomial of trust and responsibility guides the interpretation of this fundamental freedom for teachers, who should neither act as class monarchs, absolutely free of restraints, nor as hired mouth, narrowly limited to the official curriculum. The article concludes that the ethical duties of preventing harm to students and engaging in responsible pedagogy circumscribe Canadian schoolteachers' freedom of expression.