Pre-service teachers are typically supervised by two differently situated mentors: university-based clinical supervisors and cooperating teachers. These two types of supervisors are positioned differently within the institution of teacher education. Using ecological systems theory combined with institution theory, this paper offers an analytical framework for ecologically investigating how teacher supervisors and cooperating teachers are positioned and the effects on their labor, identities, and practices and how ecological forces operating at multiple levels shape new teacher learning. Drawing from empirical research to provide examples of this framework in action, the paper examines challenges to the field and offers potential responses that teacher education programs and teacher supervisors can take to mitigate these challenges.