In elementary classrooms, reading and math traditionally receive more emphasis, reducing the time available for social studies instruction (Heafner & Fitchett, 2017). However, this marginalization of social studies has a negative impact on access, equity and learning outcomes (Tyner & Kabourek, 2020). This research sought to (1) define the characteristics of elementary social studies programs in high-needs Connecticut Alliance districts and (2) explore the efforts of curriculum leaders in implementing social studies reform. These findings provide insight on how to implement high-quality social studies instruction at the elementary levels in high-needs school districts. This explanatory sequential mixed-methods study (Creswell, 2014) identified factors of successful social studies curriculum implementation at the elementary level in Connecticut Alliance Districts. Leaders reported on characteristics of their social studies programs, efforts to implement new frameworks, and positive outcomes associated with those efforts (Metz & Louisson, 2018). The research categorized districts as successful implementers, initial implementers, or pre-implementers. Data collection occurred through surveys and qualitative interviews with curriculum leaders at all implementation levels. The study is grounded in the framework for usable innovation (Blase & Fixsen, 2018). The quantitative results showed a statistically significant relationship between positive outcomes and the extent of active implementation. Furthermore, Fischer's exact tests found that curated resources and an embedded humanities instructional block had a significant relationship to successful implementation. The qualitative results demonstrated that successful implementers described extensive, teacher-centered efforts to create a shared understanding of inquiry. Data from pre- and initial implementers revealed challenges, including leadership structures and a lack of clarity about alignment to inquiry-based instructional approaches. Having a humanities block driven by social studies content with extensive writing and wide reading was central to successful implementation. The study has implications for educators and policymakers as it provides data on how the social studies community can support active implementation and stakeholder engagement. Attention to the successful implementation of social studies curriculum will benefit all students. [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.]