The need for social contact is a fundamental feature of human development. However, living together with others is only successful if one has the ability to communicate with others and adjust to them. Complex social-emotional competencies are needed to recognise and express one's own emotions and needs, but also to perceive and recognise the feelings and limits of others, to show empathy and prosocial behaviour (Petermann & Wiedebusch, 2002). Therefore, the acquisition and development of social-emotional competencies is a central developmental task of childhood.

Although the influence of the familial environment on the development of social-emotional competencies is hardly disputed, research predominantly focuses on parental characteristics or parent-child relationships. However, most individuals in Germany grow up with at least one sibling (Federal Statistical Office, 2021). Often, siblings spend more time with each other than with their parents (Onnen-Isemann & Rösch, 2005). In the process, they fight and disagree, share and cooperate, and learn to resolve conflicts among themselves. Siblings take on important socialising functions for each other. Sibling relationships, which are characterised by a lower power imbalance than for example parent-child relationships, represent a special learning opportunity for social-emotional competencies. Siblings form important social and emotional attachment figures and caregivers. Following Bandura's learning theory, siblings have some characteristics that make them more effective behavioural models than parents (Bandura, 1971). Through everyday interactions with siblings, children are provided with a context to develop an understanding of others' feelings, thoughts, beliefs and intentions.

While previous studies have mostly focused on structural characteristics such as birth order, age gap or gender constellations, the aspect of the quality of the sibling relationship is rarely considered. There is some evidence that siblings who have a positive relationship with each other interact more frequently, and thus have more opportunities to observe and learn from each other (Pike, Coldwell & Dunn, 2005). On the other hand, conflict between siblings can also provide an opportunity to express feelings, take each other's point of view and practise open communication (Brody, 1998). However, a sibling relationship that is perceived exclusively as negative is likely to have a negative impact on the development of social-emotional competencies. If there is only conflict and rivalry in the sibling relationship, this limits the possibility of learning prosocial skills or the regulation of emotions.

This paper explores the question of how the sibling relationship influences social-emotional competencies. The focus is on the perceived relationship quality, which can be classified according to the dimensions of affection, hostility and conflict resolution. For this purpose, data from the German Family Panel pairfam (Brüderl et al. 2021) are used. Analyses were done with a structural equation model with cluster-robust standard errors. The subscales prosocial behaviour, behavioural problems and emotional problems of the Strengths and Difficulties Questionnaire (SDQ; Goodman, 2005), among others, serve as indicators for social-emotional competencies.

Initial results show that controlling for socio-demographic characteristics and structural characteristics of the sibling relationship, there is a positive relationship between a sibling relationship characterised by affection and prosocial behaviour, while hostility is negatively related to prosocial behaviour. A more hostile sibling relationship is furthermore related to problem behaviour. For the scale of the emotional problems, a negative relationship with self-rated sibling conflict resolution and hostility emerges. While the age gap and the number of siblings seem to play a rather negligible role for the sibling relationship, the gender constellation is significant for the perceived sibling relationship quality. The results thus show that siblings (relationships) are a factor for social-emotional competencies that should not be neglected. The link can be explained in particular by the perceived quality of the relationship. With regard to the importance of social-emotional competencies, for example for psychosocial health (e.g., Denham et al., 2003), the view of the family environment should therefore be broadened and, in addition to parent-child interactions, sibling dynamics should also be taken into the focus of educational research.

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