This article describes the development and validation of an instrument that can be used to assess students' perceptions of their learning environment as a means of monitoring and guiding changes towards outcomes-based education. In the first phase, data collected from 2638 Grade 8 science students from 50 classes in 50 schools in the Limpopo Province of South Africa were analysed to provide evidence about the reliability and validity of the new instrument. In the second phase, two case studies were used to investigate whether profiles of class mean scores on the new instrument could provide an accurate and "trustworthy" description of the learning environment of individual science classes. The study makes significant contributions to the field of learning environments in that it is one of the first major studies of its kind in South Africa and because the instrument developed captures important aspects of the learning environment associated with outcomes-based education.