This study concerns the question how specific characteristics of real-time experiences relate to commitment change. The focus is on the real-time fulfillment of the basic needs: the need for competence, for relatedness and for autonomy. The research question was: “What is the relation between real time need fulfillment and commitment in psychology students during their practical internships?” The participants were 56 master students who did a five-month clinical internship in psychology. The participants wrote at least 19 weekly diary reports (in a period of 5 months) about the most important experience in their internship in that week, and in addition they filled in a short questionnaire. With a linear mixed model analysis, the relation was analyzed between need fulfillment and commitment on an individual and on a group level. The basic needs were found to be a relevant characteristic of experiences: need fulfillment or need frustration was described in by far most experiences. Experiences with a positive need fulfillment were related to higher levels of commitment strength than experiences that concerned frustration of need fulfillment, or that did not report need fulfillment. This pattern of relations was found in 90% of the individual participants. The experiences of the atypical 10% of the participants reflected a non-optimal relationship with their internship or supervisor.