Cooperative work is an effective strategy when team members are kept motivated and collaborate towards the achievement of a common goal. However, social loafing may significantly reduce educational gains. In this article, we analyse whether assessment-based reactive strategies that exploit existing emotional relationships between the team members are effective as a response to unequal commitment in cooperative tasks. In particular, an adaptive negotiation process that permits students to improve their grades by improving future scores obtained by free riders is suggested. Findings support that these types of strategies may have a great impact in fostering peer tutoring, student cooperation and mutual support.