The construction of knowledge is often more successful if students construct objects at the same. time. The is because artifacts can embody concepts and principles that often taught as abstractions in the classroom andtherefore remain "inert" and decontextualized in the student's mind. Yet what students may construct is severely constrained by the scale, scope and materials needed for the project. A virtual environment (VE) exists only in digital form. This means that the data from which it is constructed can represent any object or event at any scale and in almost any format, while allowing the student to interact with it in a great variety of ways. Its construction, therefore, is not constrained in any way by scale, scope or material. Students can construct anything they want, using computer modeling software, and place it in a VE. The advantages of constructing artifacts to help in the construction of knowledge are therefore extended to any subject matter at any level of abstraction. This paper analyzes a theoretical framework by describing five characteristics of effective VEs. The paper concludes with recommendations for the design of VEs.