Systems thinking is an essential cognitive skill that enables individuals to develop an integrative understanding of a given subject at the conceptual and systemic level. Yet, systems thinking is not usually an innate skill. Helping students develop systems-thinking skills warrants attention from educators. This paper describes a study examining the effects of utilising systems modelling as a cognitive tool in enhancing a group of graduate students' systems-thinking skills. A significant improvement was observed in the systems-thinking practises of the students. A theoretical rationale for enhancing systems-thinking skills with modelling and the results of the study will be discussed.