Check-in/Check-out (CICO) is a widely implemented evidence-based program for supporting students with at-risk levels of social and emotional behavior concerns. It is comprised of several core features described in the previous literature, including "practice elements," which are the specific actions that are delivered directly to students, and "implementation components," which are actions that support the implementation by adults. Practice elements and implementation components are both important to implementation but have been combined and conflated in descriptions of CICO implementation. Well-defined and differentiated practice elements could provide improved clarity in communicating implementation expectations to frontline implementers as well as support future research into essential active ingredients and measures of front-line intervention fidelity. The purpose of the present study was to distill, differentiate, and operationally define the student-facing practice elements of CICO. A panel of research experts and practice experts participated in a three-round modified e-Delphi process that led to the identification and operational definition of 19 discreet practice elements organized into five domains. Results are discussed in terms in implications for future development of measures of commitment and intervention fidelity, future research into active ingredients of CICO, and in terms of how well-defined practice elements can improve communication of implementation expectations for front-line implementers of CICO such as teachers.