The internship that preservice teachers complete early in the course of their studies paves the way for their transition from the role of student to that of teacher. It gives them a first opportunity to apply theoretical knowledge and develop practical skills, especially to improve their decision-making competences in the three-part process of teaching: planning a lesson, teaching it, and reflecting on the teaching performance (PTR). The present study addresses two research questions. First, to what extent do preservice teachers perceive themselves to be more competent in PTR after their initial teaching internship? Second, to what extent does the individual mood correlate with any reported improvement? 592 preservice teachers participated in the study. Using latent change score modelling, we found learning gains in all three dimensions of PTR. In addition, the results show that negative mood predicts processes of planning and reflecting following the internship, but has no effect on the actual teaching of the lesson.