The study examined the effectiveness of group investigation versus lecture-based instruction on students’ concept mastery and transferability in social studies learning. The researcher used an experimental design to randomly assign 116 eighth-grade students into control and experimental groups. The control and experimental group had 58 students, respectively. The researcher exposed the control group to lecture-based instruction through an oral presentation led by an instructor. On the other hand, students in the group investigation approach were grouped into groups of 6 and asked to investigate, think, discuss, and share their ideas on the topic with the class of 56 students. As the researcher hypothesized, the experimental group that the instructor exposed to the group investigation method that required learners to be active, plan, discuss, question, investigate a given topic, think, inquire, and present their findings to the class significantly outperformed the control group where learners mainly were passive listeners, on both concept mastery and transferability. Therefore, a significant difference exists between the lecture-based approach and group investigation towards promoting concept mastery and transfer performance among eighth-grade students. Based on the study results, the researcher recommends that eighth-grade social studies instructors adopt the group investigation method since it keeps learners active and also enhances transfer and concept mastery.