Experiments are of central importance for the natural sciences in general and in science education in particular, but the learning gains that teachers expect from them often fall short of expectations. This is especially true for student experiments, which are often conducted in dyads or small groups. In such a collaborative form of experimentation, the successful execution of the experiment and thus the achievement of the goals of the learning activity also depends on the cooperation of the students, so that a lack of learning success can also be caused by insufficient collaboration. In this study, mobile eye trackers were used with N=40 students to record gaze behavior during collaborative experimentation in the context of geometrical optics in order to investigate the influence of Joint Visual Attention (JVA) on learning success during experimentation. A significant relationship between JVA and learning gains was found for the setup phase with respect to experiment setup. The results show that especially during the setup of the experiment a successful collaboration of the experiment partners is of high importance for later successful execution of the experiment and thus support measures in this phase, such as the targeted directing of the attention of both experiment partners, could lead to an increase of the learning gain.