This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book deals with the question whether social exclusion by classmates lead to behaviour problems and learning difficulties of students with special educational needs (SEN). It aims to investigate whether the ordinary class attitude toward peers with a disability are related to the social participation of students with disabilities. Attitudes toward peers with a disability, as well as aspects of social participation like peer acceptance, friendships and peer interactions were assessed using questionnaires. The findings showed that on the one hand students with SEN are less accepted by their peers, have fewer friends, as well as less social interactions than their peers without SEN. The findings revealed an influence across the aspects of social participation for both, students with autism spectrum disorder and sensory and/or motor limitations compared to regular students.