Advancement in science and technology calls for enabling students making informed decisions in the context of socio-scientific issues (SSI). This study aimed at exploring the efficacy of teaching science through SSI-based argumentation for improving grade-IX students' argumentation skills with particular focus on the quality and complexity of argumentation. A pre-experiment; pre-post-test design was employed. All of the grade-IX students (n= 44) of biology group in an urban public school of Karachi, Pakistan were recruited as a sample. After being taught a unit of eight lessons (45-minutes each) on genetics, students were explicitly engaged in oral and written argumentation for further four sessions (45-minutes each). Data were collected through writing frames before, and after the intervention to gather evidence on progress, students have made in SSI-based argumentation. The data were analysed for complexity and quality of argumentation using the pre-defined analytical frameworks. The findings indicated an overall improvement in complexity of students argumentation with significant difference (Wilcoxon W = 553; Z =-4.94; p < 0.01). The magnitude of difference fell in the category of large effect (r = 0.80). Similarly, a significant difference (Wilcoxon W = 528; Z =-5.00; p < 0.01) was observed in the quality of students' argumentation with a large (r = 0.832) effect size. Moreover, a model of teaching and learning science through SSI-based argumentation has also been developed.