Emerging from a human constructivist view of learning and a punctuated model of conceptual change, these studies explored differences in the structural complexity and content validity of knowledge about prehistoric life depicted in concept maps by learners ranging in age from approximately 10 to 20 years. Study 1 (cross-age) explored the frequencies of concepts, relationships, levels of hierarchy, branching, and cross-links in concept maps drawn by students in grades 5, 8, 11, 13, and 14. The results provide some support for a punctuated model of conceptual change. Study 2 (longitudinal) explored the same frequencies on repeated occasions among students enrolled in a college course on prehistoric life, and documented the shift in frequencies of "novice" and "expert" concepts occurring during the semester. The results suggest that college students engage in much restructuring of their knowledge frameworks during the period of a semester. Together, the two studies raise questions about common classroom practices that encourage the rote learning of biology and geology concepts at all levels.