Quality improvement strategies largely focus on lead teachers’ qualifications with little regard to their work environment, while also overlooking a significant segment of the workforce—assistant teachers. Early educators work in teams, and assistant teachers play an important role planning, implementing, and supporting classroom activities. Using an explanatory mixed-methods design, the present United States based study examines assistant teachers’ (N = 436) assessments of their work environment, with a focus on teamwork. Findings reveal how features of the work environment are related to assistant teachers’ assessments of teamwork. Implications for policy, practice, and future research are discussed to address the work environment factors that support the ability of assistant teachers to collaborate and meaningfully contribute to the functioning and quality of children’s learning environment. (author abstract)