While literacy research in the area of multimodality includes a range of communication modes, the combination of the visual and verbal modes is arguably the most common multimodal text form used in classroom contexts from posters, charts and information texts to picture books and graphic novels. Assessment of students' understanding of visual and verbal modes as well as their combined meanings is a growing area of literacy research. Using data drawn from a larger case study, this article focusses on 11 middle years students (Grade 6) as they read then discussed a range of features from the award-winning picture book "The Watertower" by Gary Crew and Steve Woolman. This picture book includes visual and verbal intersections, where the meanings of each mode may be equivalent to each other, augment each other or at times apparently offer divergent or contradictory meanings. With a focus on assessing students' multimodal knowledge, comprehension and visual metalanguage, the study utilized assessment strategies which included discussion, questioning and a visual text making activity. The findings are discussed in terms of the suggested guidance for planning effective multimodal assessment strategies in the classroom.