Communicating effectively in English is crucial across the professions. Preparing English-language learners to work in digitally-complex environments requires meeting specific teaching goals related to English-language fluency and multimodal literacies, including teaching students about the range of modalities appropriate to the targeted culture-of-use. This study describes a multimodal literacy teaching project implemented in an English as an Additional Language graduate programme in technical communication, built around a multimodal assessment grid to teach instructional video tutorial design. The grid integrates multimedia learning principles into modal categories to guide students in navigating the complexities of this dynamic genre. Using a replication study, we investigate the impact of our grid on student learning by examining how professional video designers assess student-produced video tutorials across two cohorts (Y1 and Y2), only one of which (Y2) had access to the multimodal assessment grid during the design phase. We then compare Y2 student self-evaluations of their video productions with professionals’ assessments. Our study contributes to objectively measuring content and language-learning outcomes by collaborating with content specialists and proposing a robust basis for future research in multimodal literacy pedagogy.