Most teacher education programs in Germany have implemented long-term internships to foster pre-service teachers’ teaching skills. However, there is a lack of research to date regarding the effects of these internships on pre-service teachers’ actual teaching performance. This study attempts to offer insights into the performance development of physical education (PE) pre-service teachers during a 5-months internship. In total, 11 pre-service teachers were videotaped in the same class: three times at the beginning and three times at the end of the internship during PE lessons. All lessons were rated with the Classroom Assessment Scoring System (CLASS) by licensed CLASS observers. CLASS is a highly inferential rating system for the analysis of classroom observations and classroom videos. The CLASS for primary schools (CLASS K-3) assesses 10 dimensions of teacher–student interactions, which are summarized in three core domains. These core domains comprise emotional support, classroom organization, and instructional support. Interrater reliability was assessed using the percent-within-one analysis. The development of teaching performance of pre-service teachers in PE showed no significant rise in the 10 dimensions/three core domains measured over the course of the internship. Interpretations of these findings and practical implications for teacher education are discussed.