More than 1.6 million children and youth in the United States attend 21st Century Community Learning Centers (21st CCLCs), which are federally funded after-school programs available in each state, particularly for students who attend high poverty and low-performing schools (US Department of Education, 2020). These 10,125 centers are intended to do much more than provide supervision and safety for children afterschool while their parents are still at work. Their mission includes academic support and enrichment, social and emotional learning, drug and violence prevention, and physical activity and nutrition education (Afterschool Alliance, 2021). The centers do not all follow a prescribed curriculum, approach, or structure, even within their respective states, but they do all share common goals and report data on progress toward those goals (Weiss, 2013). Each state is mandated to conduct evaluations of its 21st CCLC programs, and these evaluations have grown in sophistication over the past decade (US Department of Education, 2020). However, these evaluations typically focus on mean-level outcomes, without considering the microlevel social interactions between staff and youth and among peers that are instrumental in producing those outcomes. The purpose of the present study is to explore the use of the Classroom Assessment Scoring System (CLASS; Pianta et al., 2008a) observation protocol in a statewide evaluation of 21st CCLCs and its potential to be useful in designing and targeting training and professional development opportunities for 21st CCLC program staff.