Sex-typing is a scientific phrase that refers to how children conform to their assigned gender roles, according to the Penn State News report "Siblings of Influence." Boys, for example, are commonly expected to be boisterous, outspoken and competitive. Girls are generally raised to be nurturing, passive and sensitive. Older siblings of the opposite sex, however, may influence a child's sex-typing. A girl with an older brother is more likely to be assertive and adventurous than peers who do not have this family composition. These dynamics may be different if there is another female sibling, older still than the brother. Another factor affecting sex-typing is how much the family conforms to societal gender roles overall. Households without traditional gender expectations may not exhibit vast sex-typing.

Research conducted by psychologist Walter Toman indicates that sibling positions, in addition to gender, affect likelihood of divorce. The premise is that older children are more likely to assume leadership roles, while younger siblings tend to be more adaptable. These characteristics predict compatibility. A married couple comprised of a younger sister of an older brother and an older brother of a younger sister is less likely to divorce than one consisting of a younger brother of a brother and a younger sister of a sister.

Siblings help one another socialize. They provide companionship to each other, develop effective means of communication and become aware of conflict resolution. This allows them to cultivate an understanding of how best to get their needs met, whether it be through coercion, manipulation or assertive speaking. They learn from their older counterparts how to behave appropriately at school and among their peers. Exposure to an older brother and his friends might also enlighten younger sisters regarding mysteries of the opposite sex.

Older children commonly perceive their younger siblings as having invaded their lives. They are forced to share their possessions, their homes and their parents. This infringement can rapidly lead to a bitterness, possibly extending to adulthood. Similarly, younger siblings are sometimes faced with the task of escaping comparisons to their older counterparts. "Psychologies" magazine reports that tumultuous sibling relationships can improve if both siblings commit to talking through and resolving the issues.