“…The change of populations of different species and their interdependence have been identified as emergent patterns in ecosystems (Dickes & Sengupta, ; Wilensky & Reisman, ; Wilkerson‐Jerde & Wilensky, ). The study of population growth and decay involves reasoning about the behaviors that cause populations to fluctuate, such as birth, death, immigration, competition for resources, or population density (NRC, ; Sandholm, ; Wilkerson‐Jerde & Wilensky, ). Typically, mathematical models of population growth are part of most high school curricula (NRC, ; Wilkerson‐Jerde & Wilensky, ); however, we believe that it is possible for younger children (e.g., third and fourth graders) to begin to reason productively about at least some aspects of population growth and decay.…”