Residential environmental education centers are important providers of science curriculum, offering students learning experiences outside the traditional classroom. One major criticism of these centers and other nonformal science centers is that they often do not include student outcomes in the evaluation of their programs. The purpose of this study was to examine the effectiveness of the use of concept maps as a means of documenting changes in student knowledge in order to include students in the program evaluations of residential environmental education centers. In this mixed-method study, 3rd and 6th grade elementary students created concept maps before and after a field trip to a residential environmental education center. Analyses of the maps revealed a significant increase in the number of unique ideas represented on the posttest maps. Interviews with stakeholders revealed that the maps provided center stakeholders with valuable information regarding program impact. Results of the study suggest that concept maps can be used effectively to document changes in student knowledge and may contribute to improvement in program evaluations of residential environmental education centers.