This qualitative case study explored a third grade bilingual teacher’s transformative language ideologies through participating in a collaborative action research project. By merging language ideologies theory, Cultural Historical Activity Theory (CHAT), and action research, I was able to identify the analytic focus of this study. I analyzed how one teacher and I, the researcher, collaboratively reflected on classroom language practices during the video analysis meetings and focus groups. Further, I analyzed twelve videos that we coded together to see the changes in the teacher’s language practices over time. My unit of analysis was the discourse practice mediated by additive language ideologies. Throughout the collaborative action research process, we both critically reflected on the classroom language use. We also developed a critical consciousness about the participatory shifts and learning of focal English Learner (EL) students. Finally, the teacher made changes to her classroom language practices. The results of this study will contribute to the literacy education research field for theoretical, methodological, and practical insights. The integration of language ideologies, CHAT, and action research can help educational practitioners, researchers, and policy makers understand the importance of transforming teachers’ language ideologies in designing additive learning contexts for ELs. From a methodological perspective, the transformative language ideologies through researcher and teacher collaborated video analysis process provide a unique contribution to the language ideologies in education literature, with analytic triangulation. As a practical implication, this study suggests action research can be one of the teacher education tools to help the teachers transform language ideologies for EL education.