This document analyses cooperative learning in a working group using a problem-based learning methodology. We also evaluate if the perception that each member of the group has of his/her contribution to cooperative learning is greater or lesser than that observed by his/her team-mates. Different elements of the work carried out in the group are analysed, such as the effective effort made, their participation, the organisation of the group, cohesion, communication, and the overall perception of their involvement in the cooperative learning and work. It is observed that the students perceive their contribution as greater than that perceived by their team-mates, although we find slight differences depending on the elements analysed.