Communication seems to play a pivotal role in any high school classroom. But it was found those classes or certain individual students shy away from engaging in effective communication during natural science lessons in Swaziland. One of the directives in the Swaziland National Education Policy states that syllabuses for studies in Form 4 and 5 should enable learners to develop essential skills which include communication and language skills. This study then, on realising that there was a gap between what was stated in the Education Policy and what was actually the case in the natural science classrooms, sought for a solution that would encourage effective communication in natural sciences. Therefore, the main purpose of the study was to encourage active participation of high school students in natural science lessons. The main research question posed for this purpose was: Can student motivation enhance classroom discourse for the negotiation of science understanding? Five sub-questions emanated from the main research question: (a) How does classroom discourse relate to natural science understanding? (b) What effect does external motivation have on discourse during natural science lessons? (c) What is the effect of feedback during natural science learning? (d) How can feedback be enhanced in the natural science class? (e) Which teaching strategies improve interactions during natural science learning? The study is organised into five chapters. The first chapter summarises the whole study by giving the problem statement, research aim and objectives, definition of terms, as well as chapter divisions. Chapter two provides the background to the study through the discussion of education theories based on classroom discourse and motivation. The third chapter presents detailed information about the research design, methods of data collection and analysis, as well as a proposed method for motivating students. The fourth chapter presents the research results, analysis and discussion. The fifth and the final chapter presents research findings, concluding remarks drawn from the research findings, as well as recommendations for similar future research. The case study style uses a qualitative, descriptive and exploratory approach. The study concentrated on theories explaining learning and motivation. The sample comprised six purposefully selected students and their two physical science teachers. Data were collected using the standardised open-ended interview and non-participant lesson observation methods, and from documents. The data were collected in two phases, the pre-motivation phase and the motivation phase. The collected data was further categorised into two segments, with each segment being a unit of analysis. One of the segments was composed of oral interchanges, while the other was composed of students’ written work. The data was then transcribed, coded, analysed and discussed using the thematic discourse analysis approach. The principles of triangulation, reliability and validity ensured the credibility of the study remained intact. Research ethics were also observed by the researcher and there was trust, respect and autonomy during data collection. The ethics observed included informed consent, confidentiality, beneficence, anonymity and non-malificence. Permission to collect data was sought and obtained from all concerned. The motivation method helped the physics group improve more (55%) than the chemistry group (7%) in tests. In the overall performance the two groups improved more or less the same: the chemistry group improved by 4% while the physics group improved by 5%. There were three main findings for the study and they revolved around the purpose and the research question. The first major finding was that the motivation method used with the students instilled self-discipline in the students, resulting in self-regulated behaviour and better understanding of science concepts. The finding suggested that motivated students are self-disciplined and take ownership of their learning. The second major finding was that during the motivation phase of data collection interactions improved between the students and their science teachers. These interactions were in the form of classroom talk, submission of school work and feedback. It was inferred that motivated students communicate more effectively and with better understanding of the concepts taught. The third major revelation was that the students were motivated by learner-centred teaching strategies and the use of teaching aids in a science laboratory. A main finding for the first sub-question was that the more students interacted with each other, with their natural science teachers, and with their books the more they appreciated and understood science concepts. For the second sub-question the main finding was, the motivation method used with the students improved discourse during natural science lessons. The marks the students were awarded gave them the energy to engage more in science activities and to behave well. The main finding for the third sub-question was that prompt feedback and positive comments motivated students to engage more in science discourse and to understand science concepts better. An important finding from the fourth sub-question was that prompt and positive feedback enhanced feedback, as well as giving students tasks that were not too far above their abilities, enhanced feedback in the natural science class. For the fifth sub-question it was found that student-centred teaching methods as well as teaching aids and learning in science laboratories improved interactions during natural science learning. / Curriculum and Instructional Studies / D. Ed. (Curriculum Studies)