Collaboration skills are essential for the effectiveness and efficiency of collective efforts in both professional and personal contexts. However, their complex and intertwined nature poses challenges in both defining and assessing them. To develop educational methodologies aimed at enhancing the cultivation of collaboration skills, there is a need for developing pre-post experimental assessment tools that target the construct in real-life school settings. Research indicates a lack of performance-based assessment tools designed to assess collaboration skills. This research proposes a performance-based assessment developed through collecting evidence from individuals participating in both solo and group puzzle activities. The assessment is created by viewing collaboration skills through the lens of the ATC21S framework. A total of 148 students aged from 11 to 12 years old from 12 different public schools in Greece participated in this study, carried out over a period of 7 months between December 2023 and June 2024 in both the test and retest phases. The results show that, regardless of the group compositions, individual student collaborative performance was stable. The validity of using Spearman’s correlation coefficient was measured at 0.623.