The complexity of development processes makes it difficult to observe and interpret the impacts of policies. The authors demonstrate the use and benefits of system dynamics modelling (SDM) in impact evaluation of private sector development programmes. A system dynamics model was hereby specifically used to compare the observed post-intervention situation with a hypothetical non-intervention scenario. They used the model to construct an optimal mix of interventions that supports sustainable private sector development. They found that developing a system dynamics model and ‘gaming’ with it is an appropriate means to link the behaviour of the industrial system we observe to its structural elements. This supports the understanding of the impact of complex interventions in industrial systems and can be further useful to convey lessons learned from the evaluations of complex systemic interventions.