In this dissertation, the researcher examined the effective implementation of Tier I strategies at One Team Central School District within the broader framework of Response to Intervention (RTI) and Multi-tiered System of Support (MTSS), addressing the urgent issue of Tier 1 instructional quality, particularly targeted at economically disadvantaged students. Utilizing a mixed-methods method, the research investigates the effect of professional development (PD) sessions on Grade 5 teachers' abilities to understand and implement such Tier 1 strategies as modeling, differentiation, and vocabulary development. Driven by a theory of action asserting that the collaborative effort of the district office, principals, and teachers will result in better quality of core teaching through Tier 1 interventions and ultimately facilitate academic outcomes and bridge the achievement gap, the research studies a Plan-Do-Study-Act (PDSA) cycle of 6 weeks. The latter is broken down into professional sessions focusing on modeling, differentiation, and vocabulary development. Pre- and post-surveys results and exit tickets evidence are complemented with observational data to study the professional development sessions and workshops' efficiency in enhancing the quality of teacher instructional practice. The results indicate that professional development is effective in improving teacher ability to implement Tier 1 strategies and emphasize the importance of ongoing professional learning. The dissertation concludes with practice and research recommendations and underscores the potential of well-orchestrated Tier 1 strategies for mitigating achievement gaps and advancing equity in education. [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://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]