Treatment fidelity is essential for predicting student outcomes and discerning between intervention ineffectiveness and invalid implementation. Despite its significance, research on treatment fidelity within Multi-Tiered Systems of Support (MTSS) and Response to Intervention (RTI) frameworks is limited. Despite their moderating role in intervention success, monitoring and improving fidelity in teacher implemented interventions are often overlooked. If treatment fidelity is low, then so will the effectiveness of the intervention, which ultimately negatively impacts students' access to education. Previous studies have indicated a decline in fidelity levels after a period of ten to fourteen days post intervention training. The present study assessed the effectiveness of a treatment fidelity intervention consisting of both performance feedback and reinforcement (Combined Intervention) on the treatment fidelity of four elementary school teachers who implemented IEP-based academic engagement interventions with their student. Additionally, the study sought to identify which components of the intervention package (Performance Feedback vs. Reinforcement) contributed to increased fidelity when implemented in isolation. The researcher also tracked student intervention outcomes to assess whether student performance varied as a function of their teacher's treatment fidelity. That is, did student outcomes improve when teacher fidelity was high or consistent and worsen when teacher fidelity was low or inconsistent? Using a multiple baseline design with an embedded component analysis, results showed that performance feedback alone had mixed effectiveness in increasing fidelity, and reinforcement alone also yielded variable results; however, the combined intervention (Performance Feedback and Reinforcement) consistently led to high levels of fidelity across all participants. Results are discussed in terms of the role of treatment fidelity in student outcomes and the importance of training and support for teachers aimed at improving and monitoring their treatment fidelity in classroom settings. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]