In this commentary I unpack the Pandora's Box of issues related to the assessment of English language learners' literacy skill development in multimodal classrooms. I ask how we might quantify the benefits of multimodal composing, for k-12 as well as college students, given the existing complexity of assessing ELLs' traditional literacy skills. I use a case study of a college student, as well as data from a project in a k-8 site, to explore these issues and provide some starting points for a larger public discussion. I unpack four key issues and offer approaches to address each one.