Virtual Reality (VR) is an innovative technology that has found valuable application in the field of education. However, evaluation of the effectiveness of virtual environments, especially for training and education, is still an open issue. The study described here was performed within the European SAFE Vecwit project (Virtual Environment for Construction Workers Instruction and Training), aimed at the development of a virtual environment for the enhancement of risk perception and the consequent reduction of occupational injuries in construction workplaces. An experiment was carried out to assess system's usability and educational effectiveness of the environment. The evaluation highlights some relevant issues for VR environment design.