The study analyses the extent to which the sociological message transmitted by the teachers' pedagogic practice recontextualizes the official pedagogic discourse of the natural sciences curriculum for a Portuguese middle school. Theoretically, the study is based on theories of psychology (e.g. Vygotsky), epistemology (e.g. Ziman) and sociology, with a particular emphasis on Bernstein's theory of pedagogic discourse. A mixed methodology was used in the study. The results suggest the existence of processes of transformation of the message within the Ministry of Education, when passing from the general principles to the specific principles of the curriculum. Transformation is in the direction of decreasing the quality of science education. The results of the curriculum analysis are discussed with regard to specific characteristics studied: metascientific knowledge, scientific knowledge and competences, intradisciplinary relations and evaluation criteria. The results also showed a decrease in the quality of the teaching-learning process when recontextualizing curriculum into pedagogic practices. This is shown by the absence by teachers of recognition and passive and active realization rules in most of the characteristics under study. These processes of transformation of the message are discussed, as well as its consequences in terms of scientific literacy.