Teaching Residents at Teachers College (TR@TC) is an 18-month program that prepares teachers for high-needs schools in New York City in two areas: teaching English to speakers of other languages (TESOL) and teaching students with disabilities. Student teachers, called residents, spend a year working with a mentor teacher. Mentors play three roles: teacher, field-based teacher educator, and learner. With the program entering its sixth year, there are several lessons learned. Mentors need guidance on how to teach adults, general education teachers have an important role to play, it's crucial to identify partnership schools, and positioning mentors as experts enriches the program as a whole.