As literacy researchers continue to investigate how young students make sense of texts, specifically picture books, attention has expanded beyond the role that written language plays in reading comprehension to the various ways that visual images, typography, design elements, and digital devices support and challenge young readers during the act of reading. This article is a description of classroom-based research that led to the development of an assessment instrument for classroom teachers designed to help teachers observe readers using a variety of semiotic resources to make sense of contemporary picture books. As the texts that young readers encounter continue to evolve from language-dominant texts to more complex multimodal ensembles, classroom-based assessments must evolve as well to account for the semiotic resources that young readers use in navigating and comprehending multimodal texts.