The learning analytics dashboard (LAD) has been recognised as a useful tool to facilitate teachers' diagnosis and intervention in collaborative learning. However, little empirical evidence has been reported concerning the effects of LAD on teachers in computer-supported collaborative learning (CSCL). The purpose of this study was to evaluate the effectiveness of a LAD system called the Knowledge-Behavior-Social Dashboard (KBSD) for supporting teachers' diagnosis and intervention of CSCL activities. Thirty-five pre-service teachers participated in the experiment. The results indicated that teachers using KBSD used more 'cross-group' strategies to diagnose students' learning problems. Teachers in the experimental group also performed more interventions involving 'cognitive guidance', 'scaffold instructing', 'positive evaluation' and 'individual facilitating'. Moreover, the analysis of the interview revealed that the KBSD tool has the potential to assist teachers in detecting learning problems in a group in an easy and convenient manner. Pedagogical implications and future research are also addressed.