Numerous states use research-based mathematics curricula as a teaching tool to enhance mathematics performance outcomes on state assessment scores. Despite implementation of the Eureka curriculum, students at the study site were still struggling to master Algebra 1 skills sufficiently to pass the Louisiana state exam. The aim of this basic qualitative study was to explore strategies teachers employed while implementing the Eureka curriculum to increase student achievement. The study was guided by Vygotsky's zone of proximal development (ZPD) theoretical framework and involved semi-structured interviews with 12 participants who had been teaching Algebra 1 with the Eureka curriculum for at least three years. The research question was focused on instructional strategies teachers used with Eureka to teach Algebra 1 students within their ZPD levels. Data analysis was conducted using open coding for review of themes and patterns. Identified themes included strategies to support Algebra 1 achievement, strategies that hinder student achievement, other factors influencing academic achievement, instructional strategies that were absent from the Eureka curriculum, and the necessity to enhance professional development. A professional development program was developed based on research findings to assist teachers in implementing effective strategies for the Eureka curriculum aimed at increasing students' academic performance in Algebra 1. This professional development initiative has the capacity to bring about positive social change by increasing teachers' facilitation of mathematics instruction with evidence-based strategies that increase student achievement in Algebra 1 concepts and skills. [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.]