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### The numbers

Roughly forty percent of US marriages and forty-five percent of Northern European cohabitation-to-marriage transitions involve at least one child from a prior partnership. The figure has been climbing slowly for three decades and has plateaued only because the underlying divorce rate has stabilized. About one in three children in developed countries will live in a stepfamily household before age eighteen; a similar fraction will experience two or more household transitions. These are not minority experiences. They are, demographically, the central case of contemporary family life, and the policy and cultural infrastructure has not absorbed this fact.