This study aimed to explore the interplay between 10th grade students’ decision-making abilities and their co-regulated behaviors in groups on socio-scientific issues. The mixed method was employed in the current study with convenient sampling to invite 38 students participating. They engaged in an SSI decision-making learning module collaboratively (paired in a group). The results of leg sequential analysis manifested that HIRG (higher informal reasoning groups) focused on identifying the demands of the learning task. They would set a specific goal and used strategies after clarifying the demands of the learning task. They also actively regulated their cognitive performance after some monitoring and evaluating behaviors. Students demonstrated higher informal reasoning and employed a specific decision-making strategy in groups in an SSI context if they could clarify the task demands and set a clear goal associated with actively monitoring and regulating their collaborative learning. Further, students’ co-regulation was coded as self-regulation, co-regulation, and social shared regulation. In general, the number of students’ self-regulation behaviors was identified quite few, and the number of social shared regulation were higher than that of co-regulation. HIRG attempted to perform more social shared regulation for their decision making on the SSI.