System dynamics tools claim to enhance our mental models by enabling us to understand the elements of dynamic complexity thereby improving performance in dynamic decision-making tasks. However to date these claims have not been subject to rigorous experimental testing. The main purpose of this study is to experimentally assess the long-term efficacy of system dynamics interventions in understanding complex dynamic. This is done by evaluating the effectiveness of system dynamics intervention that was provided five months prior to the current examination. The results demonstrate if (and which) elements of dynamic complexity are retained even when people are not actively involved in using system dynamics. The follow-up tests reveal that system dynamics intervention does make long-term, fundamental changes in the way people think about complex systems. Specifically, the ability to understand stocks and flows and recognize feedback loop is retained.