Context. Mindfulness is a meditation technique whose main goal is keeping the mind calm and educating attention by focusing only on one thing at a time, usually breathing. The reported benefits of its continued practice can be of interest for Software Engineering students and practitioners, especially in tasks like conceptual modeling, in which concentration and clearness of mind arecrucial. Goal. In order to evaluate whether Software Engineering students enhance their conceptual modeling performance after several weeks of mindfulness practice, a series of three controlled experiments were carried out at the University of Seville during three consecutive academic years (2013+IBM-2016) involving 130 students. Method. In all the experiments, the subjects were divided into twogroups. While the experimental group practiced mindfulness, the control group was trained in public speaking as a placebo treatment. All the subjects developed two conceptual models based on a transcript of an interview, one before and another one after the treatment. The results were compared in terms of conceptual modeling quality (measured as effectiveness, i.e., the percentage of model elements correctly identified) and productivity (measured as efficiency, i.e., the number of model elements correctly identified per unit of time). Results. The statistically significant results of the series of experiments revealed that the subjects who practiced mindfulness developed slightly better conceptual models (their quality was 8.16 percent higher) and they did it faster (they were 46.67percent more productive) than the control group, even if they did not have a previous interest in meditation. Conclusions. The practice of mindfulness improves the performance of Software Engineering students in conceptual modeling, especially their productivity.Nevertheless, more experimentation is needed in order to confirm the outcomes in other Software Engineering tasks and populations.