Implicit in "co-parenting" arrangements, say authors Gerald A. and Myrna Silver, is that the parents will bury their hostility so they can cooperate in the "child's best interests." Among options they say have worked for many divorced couples:

Small fixed block: The child moves back and forth between each parent's home in equal fixed-time blocks of, for example, 3 1/2 days. "The child remains in close proximity to both parents, and the transition may be made after school or at the end of each week."

Large fixed block: The child lives with each parent for several months, a semester or even a year at a time, visiting the alternate parent on some weekends and evenings.

Variable block: The amount of time the child spends with each parent varies in the short run -- perhaps "based upon the job commitments of the parents or the special interests of the child? -- but generally balances out over a period of time.

Unstructured movement: The child moves back and forth between the homes at no set time, though over a period the amount of time spent with each parent should roughly be equal. "The plan requires flexibility and good communication."

Parental movement: If the children are young, say the Silvers, "It is sometimes preferable to keep the kids stationary while the parents move. The child remains in a common household, and the parents alternate moving from this household to a commonly held apartment or their own separate homes."

Any "co-parenting" arrangement, they say, should be "worked out in detail and put in writing."