Task-related variance causes scores from performance assessments not to be generalizable and thus inappropriate for high stakes use. It is possible that task-related variance is due, in part, to students' inability to transfer their knowledge consistently from one assessment task to another. If this is so, then a cognitive tool such as a concept map might be useful. This study examines the effects of concept maps on the task-related variance components of Political Science performance assessments. On three in-class graded exercises, some students used concept maps while writing two essays, while other students did not. The task variance components remained unchanged across groups, but the subject main effect components increased and the subject-by-task interaction components decreased. Also, the scores from the concept mapping groups had higher generalizability coefficients than for those who did not use a concept map.