Written expression is a key component of the secondary curriculum, but many students struggle to produce effective written expression passages. However, written expression can be supported through prewriting strategies such as concept mapping. Using a counterbalanced group design, 19 secondary students alternated between using paper- or computer-based concept mapping to write compare-and-contrast essays. Students' written expression was significantly supported by concept mapping, regardless of the method. Essays were more cohesive, included relevant ideas and structure, and had an overall higher quality. Although no statistical differences existed on essay scores between each method, students expressed an overwhelming preference for computer-based concept mapping.