The ability to comprehend informal arguments is essential for scientific literacy but students often lack structural knowledge about these arguments, especially when the arguments are more complex. This study used a pre-post-test design with a follow-up 4 weeks later to investigate whether a computerised training in identifying structural components of informal arguments can improve university students' competences to understand complex arguments. The training was embedded in a constructivist learning environment and contents were based on the Toulmin model of argument structure, according to which arguments can be deconstructed into several functional components: Claim, datum, warrant, backing evidence, and rebuttal. Being able to identify the warrant is central for scientific literacy, as the warrant determines whether a conclusion is justified given the data. Results indicate that training in argument structure did not generally improve performance for all students and argument types, but that it was particularly helpful for identifying more complex arguments with a less typical structure and relational aspects between key components (i.e. warrants). High achieving students profited the most from this intervention, and the intervention was also helpful for students with high pretest accuracy scores. Our results suggest that interventions to foster argumentation skills should be included into the curriculum and these interventions should be designed to match learners' ability level.