The introduction of qualitative modelling techniques into learning environments, and intelligent training systems, requires not just the development of tools and techniques for modelling and simulation but also some guidance on how to use qualitative models in learning environments. This paper describes the rationale behind the design of a simulation based learning environment, the Model Switching PROcess rig Demonstration System (MS-PRODS). Three qualitative and three quantitative simulations of the behavior of the physical system have been implemented using the ITSIE tools (Scott et al, 1990). The design of the learning environment is presented from the point of view of instruction and how the models are to be used to promote learning, in particular examining the model switching mechanism. This mechanism determines how to select and sequence the presentation of models to the learner during guided explorations of the domain. A knowledge based an alysis of the domain knowledge is combined with principles derived from Cognitive Flexibility Theory (Spiro 6 Jehng, 1990) to produce a generic design for a learning environment based on multiple models. The design and implementation of the learning environment is illustrated and a sample sequence of models presented. Finally, related work such as White & Frederiksen (1990) on model progression is discussed.