A research report in part fulfilment of the requirements of an MSc in Science Education at the University of the Witwatersrand / This study reports the findings of a research project in a DET (Department of Education and Training)* school in Mamelodi, South Africa, in 1995. An investigrtion was carried out to ascertain whether students benefit from having access to science definitions in their vernacular, and to determine their preference in terms of the medium of instruction in the science classroom. A Science Concept Guide, written at RADMASTE** Centre, was used as the main component of the intervention in a pretest - post-test study. This was followed by student questionnaires and interviews. The Concept Guide consisted of definitions and explanations of Physics and Chemistry concepts arranged according to themes. These explanations were translated into North Sotho. Two groups of Std 10 students participated in the evaluation of the Concept Guide. One group used an English version of the Concept Guide and the other an English and North Sotho version. The differences between the pre-test and post-test scores of each group were compared. The results indicated that a significant improvement in scores had occurred in the English and North Sotho Group. Interview results showed that a number of students were in favour of having learning material of this sort available in their vernacular and claimed that they had found it helpful. In general, both groups expressed favourable comments about the Guide. Opinions about medium of instruction varied. Overall, findings indicate that further efforts in the development of vernacular material for the learning of science would prove beneficial. Although the area of policy decision is outside the scope of this study, it hopes to contribute in some way to the knowledge about the preferred medium of learning in South Africa. / Andrew Chakane 2018