<p>The main purpose of this study was to examine primary school students’ informal reasoning patterns and argumentation quality of “plastic wastes, highland tourism and hydroelectric power plant (HEPP)” socioscientific issues (SSIs). Through an embedded multi-case design of case study method, the sample of the study consisted of 30 students (10 for each grade), who were purposefully drawn from a state school in the city of Trabzon. Semi-structured interviews were conducted via three SSI-based cartoons. Students’ arguments were analyzed in regard to informal reasoning patterns (intuitive, emotional, and rational) while their quality was evaluated through argumentation analysis rubric. The findings showed that the students mostly used the emotional informal reasoning while making decisions on the foregoing SSIs. Also, it was found that the students’ informal reasoning patterns depended on type of the SSIs. For example, the students tended to use the emotional and rational informal reasoning for “plastic wastes” SSIs as compared with others. It can be concluded that an increase in grade level has diversified informal reasoning patterns and improved the quality of the students’ arguments. Further, this study reveals that SSI-based cartoons help them pose and freely depict their informal reasoning abilities and argumentation processes. Therefore, the current study recommends that future studies may encourage students to create and animate their own cartoons to improve their informal reasoning abilities and argumentation skills.</p>