Collaboration between students is particularly important in tertiary education because most courses include group activities in which they need to work together to reach a common goal. Unlike individual learning, collaborative learning involves interaction and cooperation. However, it is difficult to assess individual contributions in a group. Teachers usually collect the final product and give the same mark to all members in the group, so this may cause unfair marking and lead to conflicts in case of uneven workload. To encourage student collaboration and provide a reliable assessment system for teachers, we proposed an online evidence-based assessment system called GMoodle (https://gmoodle.eduhk.hk) with the Teaching Development Grant (TDG-T0210) in the Education University of Hong Kong (EdUHK). GMoodle provides the basic functions of Moodle plus customized features including chatroom, Wiki and real-time progress report. It is a centralized platform for students to discuss, share resources and work out the solution together. Detailed reports, such as the number of posts/replies, weekly trend of contribution, ranking in group and class, can be retrieved by both students and teachers. The objectives of this system are to promote active and collaborative learning environment through peer motivation and facilitate an evidence-based assessment for setting assessment criteria and identifying free-riders. GMoodle was launched from September 2018 to April 2019 with 337 users involving 10 courses in IT, Mathematics, English language and law in EdUHK. Quantitative and qualitative data were collected from pre/post-test survey, system log and focus group interviews. The effectiveness of GMoodle on group collaboration and assessment was evaluated by statistical analysis by SPSS using ANOVA and t-test. The results showed that the improvement of problemsolving skills and collaborative skills were statistically significance. Furthermore, decision tree was used to discover interesting