The strategy of retrofitting quality onto a prototype and evolving it into a production quality system has at best led to severe problems and at worst to a complete failure. The present work reports on an environment and methodology that supports the development of high quality prototypes that can easily accommodate changes so that the prototypes can be evolved into production quality systems. An outline of the environment incorporating an architectural mechanism and associated tools that accommodates the intertwining of algebraic specifications, known as ADTSPEC, and implementations in a modular programming language, PARADOX PASCAL, is presented. A framework for applying the environment in the context of evolutionary development is detailed. An illustrative application is also presented. It demonstrates the effectiveness of the work, to support user participation at each stage of evolution and the engineering of high quality prototypes constructed in a systematic manner, incorporating the degree of rigour that is appropriate to the clarity of requirements.