The primary purpose of this study was to investigate the effectiveness of two different types of post-instruction concept interviews: one that did and one that did not embed a concept mapping process as means of eliciting students' post-instruction conceptual understandings about the nature of, source of, and problems caused by chlorofluorocarbons (CFCs). The study also tried to determine any effect by the addition of the independent variable, student to expert Pathfinder Network Similarity Index (PFNSI) on the prediction of the criterion measure of accordance (ACCORD). The study also sought to elicit students' perceptions of the process instituted in the interviews to determine what they know. Data was collected from eighth grade physical science students and their teacher using open-ended interviews. Findings indicate an interview that embedded a concept mapping process (compared to an interview that excluded this process) did not affect statistically significant changes in the externalization of students' conceptual understandings. Another finding was that PFNSI had predictive validity for performance in the interview on the measure of ACCORD and proved to be a reliable confirmatory measure of the degree to which students held an ideal post-instructional understanding. Contains 67 references. (JRH)