Researchers have used joint visual attention (JVA) as a proxy for collaborative quality and/or performance during the last decade due to its association with both measures. However, the notion of looking at the same object does not necessarily indicate that students are solving the problem together (or learning together). We propose a complementary approach to joint visual attention by augmenting it with joint mental effort (JME). JME is computed as a cross-recurrence of the cognitive load of the peers in a dyad. We use data from 41 dyads to show the synergy between JVA and JME and the insights that they can shed in the collaborative process. The results show that in certain episodes of collaboration (characterized by the dialogue and division of labor strategy of the dyad) combining these two dual-eye tracking measures provide deeper insights about the collaborative processes and performance than JVA alone.