A project is described in which statechart modeling is applied to the development and validation of system behavior in a state-of-the-practice organization. A group of systems engineers modeled the behavior of diverse airplane systems. The lessons learned by these engineers are described and categorized as lessons about statechart modeling and lessons about tool features that do a good job of supporting statechart modeling. While statecharts provided a robust semantic with which to model behavior, the most powerful experience for the users came from their ability to see the effect of their models via the tool's dynamic simulation and interactive animation features.