Previous research has highlighted the advantages of graphical argument representations. A number of tutoring systems have been built that support students in rendering arguments graphically, as they learn argumentation skills. The relative tutoring benefits of graphical argument representations have not been reliably shown, however. In this paper we present an evaluation of the LARGO system which enables law students graphically to represent examples of legal interpretation with hypotheticals they observe while reading texts of U.S. Supreme Court oral arguments. We hypothesized that LARGO's graphical representations and advice would help students to identify important elements of the arguments (i.e., proposed hypotheses, hypothetical challenges, and responses) and to reflect on their significance to the argument's merits better than a purely text-based alternative. In an experiment, we found some empirical support for this hypothesis.