Dealing with diversity at school can be considered a key challenge for inclusive education. Since teachers’ competence has a crucial impact on successful teaching, supporting pre-service teachers in building up competence for dealing with diversity successfully is a central interest in teacher education. Therefore, university teachers must consider ways of preparing pre-service teachers for inclusive education by implementing new learning opportunities into the curriculum that deal with diversity. The research project I-BALL faces this challenge: Based on recent reviews highlighting central didactical concepts that make teacher professional development happen successfully for both pre-service and in-service teachers, this research project analyzes empirically the effect of different types of subject-specific learning opportunities in mathematics, physical education, music, and science on pre-service teachers’ competence regarding beliefs, self-efficacy, and self-reported pedagogical content knowledge about inclusive education. This research has shown that brief learning opportunities can positively affect the development of some scopes of (self-reported) pre-service teachers’ competence on inclusive education.