Multiple loci of control is one of the main affordances of tangible tabletop UIs due to their capability for simultaneous manipulation. However, there is a tension between the efficiency given by simultaneous manipulation and the need to coordinate and reflect in group activity. We implemented a central point of control to synchronize the group work and afford opportunities for equal participation in a tabletop application. In this study, we analyzed log and video data of seven groups of primary school students using a tabletop application. The results show that log data about this central control's position and rotation can be a predictor of equal participation, also helping interpret group performance. Finally, we discuss the implications of such findings, e.g., to provide teachers with useful information about group collaborative processes.