One study that’s been cited a lot in favor of Joint Custody laws is Wallerstein’s and Kelly’s five-year study which found that children who maintain relationships with both parents adjusted best after a divorce divorce.
But Wallerstein’s study conclusions were for families where “the conflict between the divorcing partners had subsided,” not for all divorced parents – which is the trouble with studies of Joint Custody outcomes looking at families which chose Joint Custody, who are likely to be more affluent, better educated and more cooperative than the average divorcing parents. In her later followup of the same sample group, Wallerstein found that the most destructive post-divorce situation for children is where the parents are extremely hostile to each other. If both parents have custody of the child, the children can end up caught in the middle, which is a terrible situation – but one that’s much more likely if courts force Joint Custody on unwilling parent(s).
There’s also the value of small children having a stable environment, and going to a single school. It’s one thing for my friend Greg, whose parents divorced when he was 12 and voluntarily chose Joint Custody. Luckily, Greg’s parents had similar incomes, making it possible for them both to live in the same school district, in walking distance of each other, with Greg having a bedroom in each home that he could wander to at will. I think that outcome was, without a doubt, the best possible set-up for all concerned in that situation.
It’s quite another thing for small child to have to live equally in two households in alternate weeks or months – small children being shuttled from home to home report feeling disoriented and unstable, and sometimes have trouble with their schoolwork and social skills. (See “The experience of children in a joint-custody arrangement,” American Journal of Orthospychiatry v51 #3) This is something two cooperative parents will be able to deal with, we might suppose – but two parents who had gone through a nasty, hateful divorce?
And how is Joint Physical Custody handled with two parents of uneven incomes (the most common thing by far), who perhaps can’t live in the same town & school system? What happens when two parents who can’t agree that the ocean is wet need to decide what kids their child is allowed to play with, or what school to send their child to? What if one parent gets a great job offer – or a great new marriage – in another state – should the other parent be required to move, too?
All of these problems are reasonably solvable when parents get along well – but among parents who cannot get along, these situations are liable to lead to harmful tugs-of-wars with the child as the rope.