[Chandrasena et. al., Vol.7 (Iss.4): April 2019] ISSN- 2350-0530(O), ISSN- 2394-3629(P) DOI: https://doi.org/10.29121/granthaalayah.v7.i4.2019.881 Http://www.granthaalayah.com ©International Journal of Research - GRANTHAALAYAH [126] Social INVESTIGATION OF THE EFFECTIVENESS OF USING SELF- DETERMINATION THEORY IN TEACHING SCIENCE FOR GRADE EIGHT STUDENTS: A CASE STUDY IN SRI LANKA Avanthi Jayarathne 1 , W. D. Chandrasena *2 1 Postgraduate Institute of Science, University of Peradeniya, Sri Lanka *2 Science Education Unit, Faculty of Science, University of Peradeniya, Sri Lanka Abstract Science is highly important as it focusses on enhancing the quality of human life. Though, science is perceived to be an interesting discipline, students’ performance in the field of school science is not very satisfactory. Self-determination theory (SDT) assumes that inherent in human nature is the propensity to be curious about one’s environment and interested in learning and developing one’s knowledge. Thus, SDT can be used to teach science effectively in classrooms to enhance students’ performance. As described in SDT, people have three innate psychological needs; competence, autonomy and relatedness. If these needs are fulfilled, the optimal functioning of human beings can be obtained. Hence, this study focused in investigating the effectiveness of using SDT in teaching “Main Biological Processes in Plants” for Grade 8 students. The study was conducted using two groups of students as the experimental and the control. The experimental group was instructed using SDT while the control group was taught using traditional method. The students’ performance, psychological relatedness, competence, and the autonomy showed higher in the experimental group compared to the control group. Thus, the results indicate that the instructional approach based on SDT is very effective compared to traditional approach of instruction in teaching science as SDT approach develops intrinsic motivation of students. Keywords: Investigation; Effectiveness; Determination; Eight Students. Cite This Article: Avanthi Jayarathne, and W. D. Chandrasena. (2019). “INVESTIGATION OF THE EFFECTIVENESS OF USING SELF-DETERMINATION THEORY IN TEACHING SCIENCE FOR GRADE EIGHT STUDENTS: A CASE STUDY IN SRI LANKA.” International Journal of Research - Granthaalayah, 7(4), 126-131. 1. Introduction Learning biological science has important implications for human society. It is really important to everyday life as it fundamentally is the systematic study of the structure and behavior of the natural and physical world through observations and experiments. It encompasses the cellular basis of living things, the energy metabolism that underlies the activities of life, and the genetic basis for inheritance in organisms in the world.