Implementation fidelity is crucial to the success of behavioral interventions. However, measuring and maintaining intervention implementation fidelity in schools' natural settings can be challenging. This article reports findings from a study examining the implementation fidelity of check-in check-out interventions at an urban school district which had recently instituted this as their first-line targeted intervention within their tiered behavioral intervention process. Check-in check-out cards from 252 elementary and middle school students were analyzed to assess the presence of 5 implementation fidelity indicators: daily implementation, subject/area consistency, established point goal, behavioral goal consistency, and score completion. Although all schools struggled to maintain implementation fidelity in some aspects of the intervention, middle schools appeared to have greater difficulty adhering to these five components of the check-in check-out protocol.