The main focus of the present study is to explore different ways of training late primary school students to make informed decisions on socio-scientific issues, namely issues that involve scientific knowledge and affect their local community and the society in general. The research design features three supplementary experiments employing a variety of data collection and data analysis methods. Experiment 1 adopts an experimental pre-test post-test design with three learning conditions (Explicit instruction, Guided Discovery and Unguided Discovery) and whole-class interventions and aims to determine the most effective learning environment for primary school students to master decision-making skills in the context of socio-scientific issues. The sample consisted of 190 11-year-old students from four primary schools in Greece and showed that Explicit Instruction and Guided Discovery were significantly more effective than Unguided Discovery. When taking into account achievement Level, though, only Explicit Instruction closed the achievement gap, while Guided Discovery favoured high-achieving students. Experiment 2 employs one-to-one think-aloud tasks with 30 students to capture their reasoning while they are making their decisions. Experiment 2 provides context to the question under study and insight as to why and how one of the learning conditions promotes better learning outcomes. The results showed that students in the Explicit instruction tended to pay more attention to the process they were following and listed the next steps, as well as they provided more explanations on their rationale when making a decision. However, they also seemed to be less independent than students assigned in the Guided and Unguided Discovery conditions asking for the teacher’s confirmation more often. Experiment 3 features thematic analysis of student’s socio-scientific views of vegetarianism that results in two thematic maps of the risks and benefits students associate with vegetarianism. The analysis showed that students hold many misconceptions about vegetarianism and that the decision-making intervention did not have a significant effect on students’ knowledge of vegetarianism.