At the turn of the 21st century, the American Law Institute, after over a decade of work, released its "Principles of Family Dissolution." Unlike other releases by that body, it was not a Restatement of the Law but a recommendation of "best practices"—what the law should be. It recognizes that judges are ill-suited to make custody determinations on their own and offers recommendations for change.

In Chapter 2, it proposes a presumption of joint custody in decision making and a sharing of time in proportion to the amount of time each parent spent caring for the child prior to the separation, called the Approximation Rule.

Like the seminal work, Beyond the Best Interest of the Child by Goldstein Freud and Solnit, published in 1973, ALI concluded that decisions relating to custody should have more to do with family historical patterns than judicial preferences. Neither Goldstein Freud and Solnit's suggestion nor that of the ALI were accepted by state legislatures or the courts. Instead, the best interests of the child remained the standard in the United States and the courts became the arbiters of that very amorphous standard.