Selective modeling is suggested as a technique that encourages designers to mix exploratory, analytical, and empirical design activities in interaction design. The co-development of models and prototypes of interactive systems is proposed to support a better balance between formal and explorative design approaches. Models serve to inform design decisions but also to analyze emerging alternatives of prototypical implementations.Task migratability is a usability design principle that describes how control for task execution is transferred between system and user. Refined flexible task allocation is rarely achievable through pure top-down decomposition as used in many model-based approaches. The paper shows at the example of HOPS models how selective modeling can be applied to develop prototypes in a deliberated evolutionary way by using models to express different viewpoints and to explore design options at different levels of granularity.