Concept maps are visual representations of knowledge structure and thought. Not enough attention has been paid to the measurement and influence of preservice teachers' knowledge structure and its development over time. This study implemented instructional scaffolding interventions in order to determine the effect on preservice teachers' knowledge structure (i.e., concept maps) and short essay responses. The study was also designed to develop a reliable method of measuring knowledge structure and to describe the characteristics of knowledge structure over time and between groups. Twenty preservice teachers enrolled at a state-supported university in the Midwest participated in the study. Participants were enrolled in one of two "Introduction to Educational Psychology" courses during the spring of 1998. A two-group, multi-variate repeated measures design was employed. Concept maps and short essay responses were compared over time. The findings suggest that instructional scaffolding interventions have, over time, a positive effect on students' ability to: create broad categories with subsuming structures; apply key terminology; construe interpretable patterns; decipher the demands of the task; reference the content discussed; and ultimately, produce superior essays. (Contains 9 figures, 5 tables, and 3 appendices.) (SM)