Concept maps were first developed in our research program in 1972 as a way to represent changes in children’s understanding of science concepts over the 12-year span of schooling. We were using modified Piagetian clinical interviews to assess changes in their knowledge over time, but we found the interview transcripts were too difficult to analyze for changes in specific aspects of the children’s knowledge. Instead we prepared concept maps from the interviews, two of which are shown in figure 1. They illustrate the specific changes in this child’s understanding of the particulate nature of matter from grade 2 (7 years old) to grade 12 (17 years old).