Indiana University-Purdue University Indianapolis (IUPUI) / Assertive Community Treatment (ACT) is a widely implemented evidence-based practice for consumers with severe mental illness. However, fidelity to the model is variable and program drift, in which programs decrease in fidelity over time, can occur. Given substantial variability in fidelity and program drift in evidence-based practices, a study to examine how to re-implement ACT to high fidelity on established teams was warranted. The present study examined three teams providing moderate fidelity services prior to a state-wide policy change to the definition of ACT. Two of the teams attempted to implement ACT in accordance with state standards, while the third team served as a quasi-control for factors related to other state policy changes, such as a change to the funding mechanism. The implementation effort was examined using qualitative and quantitative measures over a 14-month period at a large, psychosocial rehabilitation center. Themes that were common across all three teams included the perceived negative impact of fee-for-service, ambiguity of stipulations and lack of guidance from the Department of Mental Health (DMH), difficulties with the managed care organization, importance of leadership within the agency, and familiarity with the services. Perceived barriers specific to the implementation of ACT standards included DMH stipulations, staff turnover, lack of resources, and implementation overload, i.e., too many changes at once. One team also had the significant barrier of a misalignment of requirements between two funding sources. Staff attitudes represented both a facilitator and a barrier to ACT implementation, while management being supportive of ACT was viewed as a major facilitator. One of the two teams seeking ACT status was rated at high fidelity within 6 months and maintained high fidelity throughout the study. The other team seeking ACT status never achieved high fidelity and decertified from ACT status after 6 months. The agency’s focus on productivity standards during the implementation effort hampered fidelity on the two teams seeking ACT status and greatly contributed to burnout on all three teams. The team achieving ACT status overcame the barriers in the short-term; however, DMH requirements may have threatened the long-term sustainability of ACT at the agency.