Informal learning environments such as Natural History Museums can introduce visitors to a variety of topics in evolution by providing accessible representations of concepts like geological time, evolutionary mechanisms, biological diversity, geological time, and fossil dating. Our study examined sixth-grade students' conceptualization of evolutionary ideas following four extracurricular, evolution-themed "Science Days" at Nature Campus--an informal learning environment that employs an extensive combination of resources, including fossils, mounted specimens, and labs, as well as zoological and botanical gardens. The purpose of this study was to identify changes in the students' personal constructs over time, in order to determine which aspects of what they had learned during the Science Days had been retained. I, therefore, conducted two sets of interviews, which employed Kelly's Repertory Grid technique to elicit "personal constructs" representing these students' perceptions of evolution and the concepts and ideas associated with it. The first round of interviews was held immediately after the program's conclusion, and the second was conducted 3 years later (ninth-grade). I then compared the results of the two sets of interviews. Our results showed that multiple elements of the Nature Campus learning experience were retained by the students, emphasizing the contribution of its characteristics as an authentic learning environment that uses visualization, tactile, physical examples, and interactive, inquiry-based activities to promote meaningful learning. They also showed changes in the prominence and complexity of certain constructs that reflect the nature of the relationship between what the students learned in the informal environment of the Nature Campus and what they have since been taught (or not been taught) in the formal environment of their school.