This article explores how arguments are made in student essays through the use of writing and visual resources. The data set comprises 54 essays with a passing grade from students in their final year of upper secondary school in Sweden. The data is analysed using a multimodal approach to knowledge representation on arguments in essays, involving analysis of textual composition and content in both written text and visual resources. The study gives an insight into how students design essays in relation to academic requirements, how their arguments realise epistemological commitments, and what affordances are given through the use of writing and visual resources. The results reveal that academic argumentation varies considerably between the essays. There is an overrepresentation of written and declarative knowledge in the essays, where the arguments are grounded in various web-based sources, and visualisations are used for making conceptualisation and classification more salient in writing. Both written and visual resources offer affordances in the making of arguments on the bases of the modes for communication. This article concludes that there are many high demands of knowledge defined for the task of preparing for higher education, which are not easily represented in the students' arguments in essays.