This study explored students' ability to evaluate their learning from a multimedia inquiry unit about the causes of global climate change. Participants were 90 sixth grade students from four science classrooms. Students were provided with a text describing the causes of climate change as well as graphs showing average global temperature changes. Half of the students also received an analogy to help support their understanding of the topic. Results indicated that overall students were over-confident about how much they learned and how well they understood the topic. Further, the presence of an analogy led to higher levels of overconfidence. Results also indicated that students with better graph interpretation skills were less overconfident even when the analogy was present. These results suggest that the presence of graphs and analogies can negatively affect students' abilities to accurately judge their own level of understanding and may lead to an illusion of comprehension.