Adolescent interpersonal relationships, social support and loneliness in high schools: Mediation effect and gender differences

•Opposite-sex, teacher–student and same-sex relationships influenced boys’ loneliness.•Same-sex relationships influenced girls’ loneliness.•Social support mediated the pathway from interpersonal relationship to loneliness.•Same-sex relationships had stronger effects on loneliness for boys than for girls.•Different interpersonal relationships contribute differently to loneliness. The purpose of this study was to explore the associations between the qualities of different types of relationships in school, social support and loneliness in adolescence. Using a sample (N=1674) of adolescent students randomly selected from middle schools, we found boys’ loneliness was influenced by the qualities of opposite-sex, teacher–student and same-sex relationships, whereas girls’ loneliness was only influenced by same-sex relationships. Additionally, social support mediated the association between same-sex relationships and teacher–student relationships, and loneliness. Further, the quality of same-sex relationships showed stronger association with boys’ loneliness than girls’. Finally, the quality of same-sex relationships showed the strongest association with boys’ loneliness comparing with opposite-sex relationships and teacher–student relationships. These findings are discussed to illuminate the possible mechanisms by which interpersonal relationships could influence loneliness. In future research, causal relationships and other influencing factors on loneliness should be examined.