United States courts have generally stated that their primary concern in child custody cases is the interests of the child. Many different rules have been established in the name of the interests of the child. During the nineteenth century, courts in this country were split over whether the mother or the father generally would be the better custodian for the child, with some courts recognizing a preference for the father and others, a preference for the mother. Most states eventually adopted a preference for the mother in custody cases involving children "of tender years." During the 1970's, many states rejected the maternal preference, and a substantial majority of states adopted a case-by-case best interests of the child rule. Under the case-by-case rule, the trial judge determines the custody placement that will be in the best interests of the individual child, based on all factors, with no preference given to either parent based on his or her sex.
Robert F. Cochran Jr.,
The Search for Guidance in Determining the Best Interests of the Child at Divorce: Reconciling the Primary Caretaker and Joint Custody Preferences,
U. Rich. L. Rev.
Available at: https://scholarship.richmond.edu/lawreview/vol20/iss1/2