Public Schools across the US face a common challenge in supporting minoritized students reach high academic standards. Standardized assessments repeatedly demonstrate Latinx and English Learner populations are underserved by US schools, reflecting the need to improve equitable access to high-quality instruction with a focus on diverse and multilingual learners. Dual Language (DL) models have potential to address opportunity gaps, building upon students' assets by developing academic bilingualism and biliteracy. This dissertation in practice focuses on improving Latinx students' and English Learners' access to effective mathematics instruction in a DL model. Using an Improvement Science framework, I facilitated a professional development sequence for DL math teachers in three cycles of Plan, Do, Study, Act (PDSA). In each cycle, teachers were presented with specific techniques recommended by the National Council of Teachers of Mathematics (NCTM) and aligned to Guiding Principles for Dual Language Education. To determine how the intervention impacted instruction, I analyzed qualitative data collected through classroom observations and teacher interviews. Teachers were more likely to implement concrete, visible strategies connecting mathematical representations. Students infrequently engaged in math dialogue, explaining reasoning, or persevering through struggle. As for DL strategies, most teachers incorporated language objectives and a variety of student groupings. However, few lessons included purposeful cross-linguistic connections, though these were more common in Spanish math instruction. New teachers were least likely to implement newly-learned practices. Teacher interviews revealed specific challenges impacting their use of new strategies. New teachers were overwhelmed, and expressed needing more planning time. Lack of comfort with math content and curriculum were also barriers. Interviews and observations confirmed that classroom management influenced teachers' infusion of effective math and DL practices. Findings from this dissertation have important implications for leaders and educators. Aligning with prior literature, this DiP reinforces that student behaviors indicative of deep math learning require shifts from teacher-directed to student-centered instruction. Further, it is important to foster math classroom cultures that encourage students to make mistakes, celebrate perseverance, explain their thinking, and view struggle as part of learning. Establishing these norms for all students can interrupt the traditional teaching practices perpetuating disparities in math outcomes. [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.]