This study aimed to examine elementary teachers' perspectives on implementing Tier III instruction within the multitiered system of supports-Response to Intervention (MTSS-RtI) and how the perception of efficacy influences the effectiveness of their instruction. The mixed-method interpretive phenomenology study took place in a public school district in the mid-Atlantic region of the United States. A purposeful sampling technique was used to select survey participants. Interview participants were selected using randomized sampling. The study utilized thematic analysis to identify ideas common to participants with similar experiences with the phenomenon of the study. Quantitative findings showed that most teachers strongly believe in the positive impact of the MTSS-RtI. Qualitative data results noted that the framework's impact is unclear to teachers due to the high number of unqualified staff providing interventions. Findings from the study will enrich the existing body of knowledge on teachers' perceptions, especially concerning providing Tier III interventions using the MTSS-RtI principles and practices. [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.]