This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues.Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. Over the last decades, worldwide educational policies concerning the education of students with special educational needs (SEN) have shifted in favor of inclusive education. In current literature, students with SEN are defined as ''students with various (combinations of) difficulties in participating in education (Pijl, Frostad, & Flem, 2008, p. 389)''. As stated in Article 24 of the Convention on the Rights of Persons with a Disability of 2006, inclusive education aims to provide effective individualized support in environments ''that maximize academic and social development, consistent with the goal of full inclusion'' (United Nations, 2006). Belgium is one of the states that signed the Convention. In the federal state of Belgium, each community has its own education system (De Ro, 2008). Flanders, the Dutch-speaking region of Belgium, has long been known for its two-track education system (i.e., special and regular education system are two distinct systems; Meijer, 2003). The goals of this study were twofold. The first aim was to explore loneliness prevalence in typically developing students, students with ASD and students with motor and/or sensory disabilities in mainstream 7th grade in Belgium. The second aim was to explore the relations between number of friends, friendship quality, social self-concept on the one hand and loneliness on the other for each of these three groups, and to compare them across groups. In this study, 108 students with special educational needs (SEN; i.e., 58 students with ASD and 50 students with motor and/or sensory disabilities) were matched to 108 typically developing classmates. Students with ASD reported more loneliness than typically developing students and students with motor and/or sensory disabilities. Loneliness prevalence for typically developing students and students with motor and/or sensory disabilities did not differ significantly. Factors related with loneliness differed between typically developing students and students with SEN (i.e., students with ASD and students with motor and/or sensory disabilities). For students with SEN, same-sex social self-concept was related with loneliness, but not, as for typically developing students, number of friends and opposite-sex social self-concept. Also friendship quality had a marginally significant effect on loneliness feelings for students with SEN. Implications for further research and practice are discussed. ß