This study examined the concurrent validity of concept maps as vehicles for documenting and exploring conceptual change in biology. Students (N = 91) who enrolled in an elementary science methods course were randomly assigned to one of two treatment groups. Subjects in both groups were administered a multiple-choice/free-response inventory which assayed their knowledge of “Life Zones in the Ocean,” and then were asked to construct a concept map on the same topic. Those in the experimental group subsequently received 45 minutes of computer-assisted instruction on marine life zones, while those in the control (“placebo”) group received an equivalent exposure to an unrelated topic (“Body Defenses”). Upon completing the instructional sequence, subjects were again administered the “Life Zones” inventory and asked to develop a postinstruction concept map on marine life zones. The data analysis employed a split plot factorial design with repeated measures. Differences among treatment groups were documented by analysis of variance and chi-square procedures. Subjects in the experimental group showed evidence of significant and substantial changes in the complexity and prepositional structure of the knowledge base, as revealed in concept maps. No such changes were found in the control group. Results suggest that concept mapping offers a valid and potentially useful technique for documenting and exploring conceptual change in biology.