Structural knowledge is a pre-requisite to valid performance assessment scores because structural knowledge leads to better transfer. Better transfer will cause consistency to occur between task performances for a given individual, and this consistency allows for less construct-irrelevant variance and more construct-relevant variance to be present in the scores. This means more valid scores. This paper provides empirical support for each link in this argument. Concept maps are used as representations of the structural knowledge taught in a Political Science I course. Students in that course (approximately 325 students) were assessed using an essay performance assessment. Those students in the concept-mapping condition are shown to write more consistent essays than those who do not use a concept map while writing. That is, the amount of task-related variance is related to the immediacy of having constructed a concept map. Structural knowledge is, therefore, a pre-requisite to valid performance assessment. (Contains 1 figure, 5 tables, and 88 references.) (Author/SLD)