Joint physical custody means both parents share physical possession of the child and both have an equal stake in making decisions about the child’s welfare, education, health care and religion.

Shared or joint physical custody does not mean equal or 50-50. It can mean, Zinner says, summers with the father and the school year with mother or "switching homes every other day." Indeed, parents attempting joint custody frequently have wide latitude in structuring their own parenting plans.

For most of the last century, judges had been guided by what is called the Tender Years Presumption and the Maternal Preference, both of which asserted that, all other factors being equal, young children, those who are under 13, should be awarded to the mother. The Tender Years Presumption and the Maternal Preference reversed early English common law that routinely awarded the children of divorce to the father, yet a majority of the states recognized this presumption. In the latter half of the twentieth century, courts and legislatures began to reverse decisions and repeal laws that recognized the Tender Years Presumption in favor of gender-neutral considerations refracted through the prism of the best-interests standard. Some courts have held that the Tender Years Presumption violates the Equal Protection Clause of the Fourteenth Amendment.

In other words, legal thinking about the custody of the children of divorce has migrated from a default that favored the father, to a presumption that favors the mother, and now to the wisdom of the court, which automatically favors neither.

Child custody and visitation battles remain a common feature of many bitter divorces, but a mother cannot automatically assume she will be awarded custody of the children in contested cases. In the event of a dispute, a mother must prove to the court that her custody is in "the best interest of the child." In practice, unfortunately, this often means documenting the shortcomings of her estranged husband.

It should be noted that judges tend to use the best-interest standard in a way that works to the benefit of women when child custody is contested. In 90 percent of the divorces involving minor children, courts award physical (or primary) custody to the mother, who becomes the custodial parent, and visitation rights (now often called "parenting time") to the father, who is the noncustodial parent and who also pays child support.

However, when couples cooperate, courts increasingly award joint custody because the routine puts childrearing upon the shoulders of both parents. In fact, as mentioned more than 30 jurisdictions now work from a presumption that joint custody is in "the best interests of the child."