This paper examines a professional learning (PL) program for upper elementary teachers focused on developing instructional practices to support multilingual learners (MLLs) in science. The PL sought to support teachers' praxis, which we describe as their sense of agency to critically analyze and take action against barriers to MLLs' opportunities to learn. We analyzed pre-PL interviews with teachers to identify the ways that they framed MLLs from asset- and deficit-based perspectives and the barriers that they identified that undermine MLLs' science learning. Then, we analyzed the extent to which the teachers' participation in the PL shifted their framing of MLLs and fostered their sense of agency to challenge the barriers faced by MLLs. We found that teachers shifted toward more asset-based views of students' existing language resources and deepened their sense of agency to employ scaffolds that engage these resources in their own instructional practice. However, teachers continued to surface barriers in their organizational contexts, including the emphasis placed on standardized language assessments and the misalignment between English language instruction and science learning. Our analysis shows that the PL did not adequately support teachers in navigating these particular institutional barriers. Based on our analysis, we argue that teachers and science education researchers should expand their focus beyond teachers' instructional practices and work together to remove barriers for MLLs in the larger organizational systems of schooling.