Recent reform efforts in science education include a focus on science practices. Teachers require support in integrating these practices into instruction. Multimedia educative curriculum materials (MECMs), digital materials explicitly designed to support teacher learning, offer one potential resource for this critical need. Consequently, the authors investigated how teachers used MECMs and whether that use impacted their beliefs about the practice of scientific argumentation. They conducted a randomised experimental study with 90 middle school science teachers in the USA. Control and experimental groups taught the same curriculum, using a web-based teacher's guide. Additionally, experimental teachers received MECMs including 24 videos and 17 interactive reflective prompts. The authors collected multiple data sources: pre-surveys, backend website curriculum use, self-report curriculum use and post-surveys. Results suggest that enacting a curriculum with a focus on argumentation is associated with positive changes in teachers' beliefs about this practice. Furthermore, the authors observed a wide range in how teachers used the curriculum. In terms of self-efficacy, this differential use was associated with differences in changes to teachers' beliefs about argumentation. Teachers who enacted more lessons became more confident in their ability to teach argumentation. Additionally, experimental teachers had smaller improvements in self-efficacy, perhaps because the MECM videos problematised what teachers thought counted as argumentation.