The goal of this observational study is to investigate the specificity of the growing up process in young people with disabled siblings. The functioning of adolescents with disabled siblings as a person growing up in three environments will be examined: family, peers and school.

The main questions it aims to answer are:

• Does having a disabled sibling influence the functioning of a healthy child in the family system?
• Do siblings of disabled children show a higher level of maturity than their peers with properly developing siblings?
• Does having a disabled sibling modify a child's functioning among peers?
• Does having a disabled sibling modify healthy adolescent's educational experience?
• Is there a greater risk of psychological disorders among siblings of disabled children than among siblings of normally developing children?

The 160 participants' dyads will take part in the study: healthy adolescent having disabled sibling and one of his/her parents. The parents' participation is necessary to assess the presence of possible internalizing and externalizing disorders among adolescents taking part in the study. The healthy adolescent will be filling out questionnaires regarding the remaining studied variables: functioning in the family - siblings relations, parental attitudes; at school - school achievement, extracurricular activities; relations with peers - time spending with peers, number of friends, as well as the growing up process trajectory - parentification and the way of going through an adolescent crisis.

Researchers will compare four groups (40 dyads in each group): three groups of adolescents having disabled sibling 1) intellectual disability, 2) motor disability, 3) chronic somatic disease, and 4) control group - healthy adolescent having sibling without any disability, to see if they differ from each other referring to the studied variables.

Background: Having a disabled sibling can be a source of extremely important and enriching experiences that foster both, the development of socio-emotional competences, as well as broaden the child's perspective and knowledge. However, the presence of the disabled child in the family, also poses many challenges for their siblings, especially in adolescence. Thus, having a disabled sibling is analysed in the literature from two main perspectives: threat and opportunity for development: 1) Children with disabled siblings often receive less attention from their parents and friends. They often experience a sense of injustice and anger, which may then result in hyperactivity, irritation and aggression manifested in school and peer functioning. Research also indicates that adolescents in this group exhibit higher levels of depression, separation anxiety, and internalizing behaviors. 2) The resource perspective, in turn, indicates a higher sense of responsibility, self-efficacy and pride in caring for sick siblings. There is less quarrel and competition among siblings, increased level of empathy, as well as an increase in self-control, tolerance and understanding are observed in siblings of children with disabilities.

Current scientific research on the functioning of families with a disabled child has focused mainly on relations with parents, parental roles, teachers, and medical staff surrounding the disabled child. The role of siblings has been limited. Therefore, the aim of the project is to investigate the specificity of the growing up process in young people with disabled siblings. The functioning of adolescents with disabled siblings as a person growing up in three environments: family, peers and school will be examined.

Participants: 160 participants' dyads will take part in the study: healthy adolescent having disabled sibling and one of his/her parents. Participants will be divided in four groups (40 dyads in each group): three groups of adolescents having disabled sibling 1) intellectual disability, 2) motor disability, 3) chronic somatic disease, and 4) control group - healthy adolescent having sibling without any disability, one of the parents will take part in the study together with every teenager.

Methodology: The proposed research model focuses both, on the difficulties associated with having a disabled sibling (e.g. possible occurrence of disorders), as well as resources (e.g. the higher quality of relationships in the family, especially in the sibling subsystem). The parents' participation is necessary to assess the presence of possible internalizing and externalizing disorders among adolescents taking part in the study. The healthy adolescent will be filling out questionnaires regarding the remaining studied variables: functioning in the family - siblings relations, parental attitudes; at school - school achievement, extracurricular activities; relations with peers - time spending with peers, number of friends, as well as the growing up process trajectory - parentification and the way of going through an adolescent crisis.

Inclusion Criteria to the groups having disabled sibling:

• age between 16 and 18 years;
• having disabled sibling, depending on the group: with intellectual disability or motor disability or with chronic somatic disease (diabetes);
• participation in the study of one of the parents.

Inclusion Criteria to the group having sibling without disability (control group):

• age between 16 and 18 years;
• having healthy siblings without any disability;
• participation in the study of one of the parents.

Exclusion Criteria to the groups having disabled sibling:

• siblings with multiple disabilities, e.g. intellectual and motor disabilities.

Exclusion Criteria to the control group and groups having disabled sibling:

• being an adolescent with disability/disorder/disease;
• age below 16 and above 18 years.

Polish adolescents having sibling.