The spiritual formation of teachers in Church-based schools is of great importance but doesn't always receive the attention it deserves. In the 1920s and 30s, the British writer in spirituality, Evelyn Underhill (1875-1941), gave three Addresses to teachers and one lecture at Oxford University, discussing the teacher’s spiritual life, and the importance of modelling spiritual vitality to students. Her insights still have incredible resonance nearly a century on. In this article we explore Underhill's principles concerning the teacher's spiritual life. Underhill reminds us that teaching is primarily about formation of students rather than simply imparting information. This view is supported by Parker J. Palmer and James K. A. Smith, whose ideas provide the theoretical undergirding for this article. Underhill reminds us of three movements of the soul that are important for teachers: adoration of God, communion with God and our co-operation with God in his work in our students’ lives. Remembering that we are participating in God's work as teachers and co-operating with God is a fundamentally important principle for understanding our work as teachers. Given Underhill saw spiritual discernment as important for teachers, Henri Nouwen's insights regarding spiritual discernment and its cultivation are briefly discussed. Given teaching is a spiritually, emotionally and physically draining vocation, Underhill argues it's important that we maintain hidden foundations through a rich life of prayer - drawing upon Jesus’ “Living Water” so we're like a “reservoir”, rather than a “canal”. The importance of Sabbath rest, private prayer practices, spiritual reading and “lectio divina” are outlined as practices that can help safeguard against exhaustion and burnout. Underhill's words to teachers are a practical reminder of the importance of being spiritually vibrant, so we can most effectively model Christ-like behaviour and spiritual nurture our students. The spiritual formation of teachers has the potential to positively impact teachers’ engagement with the "mission" of faith-based schools (and higher education providers), particularly differentiated curriculum, school culture, plus our broader professional identity and practice.