The purpose of this paper is to propose a framework to guide the study of classroom factors that promote student functioning and development within classroom settings. First, we describe a new framework, "Classroom Carrying Capacity," to categorize factors in the classroom as limiting or resource factors across four domains: external, collective classroom, student, and teacher. We also describe a schema for categorizing each limiting or resource factor as density dependent vs. independent and psychosocial vs. physical. This new framework is built from a model of sustainable ecosystems from the fields of biology and environmental sciences, to conceptualize the optimal level of support that a classroom can provide. Second, we illustrate the application of "Classroom Carrying Capacity" by demonstrating how three areas of research inquiry may be advanced via this framework. Finally, we recommend directions and high-leverage opportunities for theoretically and empirically building on the proposed framework.