ABSTRACT Computer-supported collaborative learning (CSCL) seeks to improve students’ learning with the support of technology. Although CSCL facilitates an enriching environment for cooperation, CSCL activities might be affected by asymmetrical participation. Group awareness tools have proven to enhance learners’ interactions, balancing the levels of participation and increasing the learning outcomes. This study investigates the effect of a group awareness tool (GAT) on participation within synchronous CSCL activities in the context of extracurricular activities. We designed a quasi-experimental within-subject study (GAT exposure and control condition) and tested an ad hoc GAT in a web-based CSCL platform with high school students (N = 140). The measured variables included the effect of the GAT on students’ participation and the quality of discussion. A complementary analysis evaluated students’ perceptions of the tool. Results revealed that the implementation of a GAT encourages students to take part in CSCL discussions without explicitly hindering its quality. Even so, the balance of participation was not significantly affected. Students further reported that they found the GAT useful to regulate collaboration. The results from the study provide further knowledge of the functioning of group awareness tools in secondary education and share an insight into how students perceive them.