During the era of accountability in K-12 schools in the U.S., school leaders' and teachers' responsibilities concerning language proficiency assessments extend beyond test administration and determination of eligibility for services. State and federal accountability systems challenge educators and school leaders to use language assessment results in meaningful ways. School leaders and classroom teachers look to English learner (EL) teachers for support given their specialized training and knowledge of language acquisition. However, sufficient language assessment literacy is critical for accurately interpreting, communicating, and using large-scale language assessment results. Extensive studies on language assessment literacy provide models to conceptualize it and ways to measure it while also pointing to the need for further development. Likewise, the limited research on language assessment use points to the decisions that results inform and the impacts they have on students and their educational experiences. Despite this work, there is still a gap in the field regarding how to develop teachers' language assessment literacy and support their use of large-scale assessment results in diverse and complex contexts. Educators and school leaders seek meaningful and actionable data from large-scale language assessment results. Future studies need to investigate approaches to strengthen educators' language assessment literacy and support their appropriate use of these results. Using a design-based research approach, this study explored the language assessment literacy and large-scale assessment use of EL teachers. It also explored the ways their practice could be mediated through the implementation of scaffolds. EL teachers were invited to participate as collaborators in iterative cycles of design to enact, analyze, and revise the scaffolds. This study was structured into four phases, beginning with a document review, followed by initial interviews, a workshop series, and culminating with follow-up interviews. The interviews followed a semi-structured format and included assessment use tasks. The workshop series integrated professional learning with the enactment of the scaffolds and included debriefing sessions for the analysis and revision portions of the design cycles. Findings suggest that designed scaffolds, in combination with embedded professional learning and implementation support, can mediate teacher practice and language assessment literacy. However, findings also indicate that the solution is not as straightforward as providing teachers with appropriate and well-designed scaffolds. This study shows that scaffolds' mediational effects can be constrained by local contextual factors such as time and EL teacher responsibilities and a lack of available collaborators and in-district support. Although not a complete solution, this study shows that deliberately designed scaffolds are a resource that empowers EL teachers to lead the work of meaningfully using large-scale language assessment results in their districts. The findings from this study also point to implications for those involved with large-scale language assessment. First, leaders of assessment consortiums and state-level departments of education should work with test developers to develop training materials and resources that are accessible and meaningful to the educators using them. This includes being mindful of the varied conditions in school contexts. Likewise, training should include job-embedded professional learning and implementation support to ensure that lingering questions and misconceptions are addressed in a timely manner. Next, district leaders should take an active role in EL programming and build their capacity with the interpretation and use of large-scale language assessment results so that they can support their teachers in this work. Furthermore, leaders should ensure that the infrastructure to support professional learning and teacher collaboration is in place, especially in districts with a single or few EL teachers. Finally, EL teachers should build a team of collaborators including supportive administrators and content teachers and other EL teachers. Likewise, EL teachers need to be persistent in seeking the clarity and information they need to accurately interpret, communicate, and use large-scale language assessment results. [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.]