Student reflective ideas were examined with respect to Group Investigation (GI), which was employed in 11 th grade Korean earth science classrooms. A modified GI method was implemented during the course of an action research effort consisting of two yearlong projects. Students' writings, which had been produced twice a year, were analyzed to reveal their reflections concerning the GI method. The students were positive about how GI altered the ways their learning occurred in the classrooms. They also reported several positive learning outcomes resulting from the GI implementation. However, there were some students who considered the GI method inappropriate for them. At times, students had difficulties and experienced problems arising from implementing GI. Implications for use of cooperative inquiry learning methods in science classrooms are elaborated on and discussed.