What is the standard that guides the judge’s decision?

Welfare of the child. The dominant principle in all child custody actions, including actions to modify custody, is that custody will be awarded to the person or institution who “will, in the opinion of the judge, best promote the interest and welfare of the child.” This language from the statute about the judge’s opinion gives the judge an enormous range of discretion as to the factors the judge actually considers as bearing on the child’s best interests and as to the weight the judge assigns to each of these factors.