Previous research on adoption has led to assumptions that indicate that there is a heightened risk in terms of psychological development and social relationships for adoptees. Yet, such assumptions have been clarified as flawed due to methodological failures. But more recent studies have been supportive in indicating more accurate information and results about the similarities, differences and overall lifestyles of adoptees.[125]
Adopting older children presents other parenting issues.[101] Some children from foster care have histories of maltreatment, such as physical and psychological neglect, physical abuse, and sexual abuse, and are at risk of developing psychiatric problems.[102][103] Such children are at risk of developing a disorganized attachment.[104][105][106] Studies by Cicchetti et al. (1990, 1995) found that 80% of abused and maltreated infants in their sample exhibited disorganized attachment styles.[107][108] Disorganized attachment is associated with a number of developmental problems, including dissociative symptoms,[109] as well as depressive, anxiety, and acting-out symptoms.[110][111] "Attachment is an active process- it can be secure or insecure, maladaptive or productive."[112] In the UK some adoptions fail because the adoptive parents do not get sufficient support to deal with difficult, traumatized children. This is a false economy as local authority care for these children is extremely expensive.[113]

As the idea of institutional care gained acceptance, formal rules appeared about how to place children into families: boys could become apprenticed to an artisan and girls might be married off under the institution's authority.[19] Institutions informally adopted out children as well, a mechanism treated as a way to obtain cheap labor, demonstrated by the fact that when the adopted died, their bodies were returned by the family to the institution for burial.[20]

Adoptions can occur either between related family members, or unrelated individuals. Historically, most adoptions occurred within a family. The most recent data from the U.S. indicates about half of adoptions are currently between related individuals.[78] A common example of this is a "stepparent adoption", where the new partner of a parent may legally adopt a child from the parent's previous relationship. Intra-family adoption can also occur through surrender, as a result of parental death, or when the child cannot otherwise be cared for and a family member agrees to take over.
In some countries, such as the United States, "Homecoming Day" is the day when an adoptee is officially united with their new adoptive family.[196] In some adoptive families, this day marks an especially important event and is celebrated annually from thereafter. The term Gotcha Day is also used to refer to this day. Many adopted people and birth parents find this term to be offensive.

During the same period, the Progressive movement swept the United States with a critical goal of ending the prevailing orphanage system. The culmination of such efforts came with the First White House Conference on the Care of Dependent Children called by President Theodore Roosevelt in 1909,[33] where it was declared that the nuclear family represented "the highest and finest product of civilization" and was best able to serve as primary caretaker for the abandoned and orphaned.[34][35] Anti-institutional forces gathered momentum. As late as 1923, only two percent of children without parental care were in adoptive homes, with the balance in foster arrangements and orphanages. Less than forty years later, nearly one-third were in an adoptive home.[36]

Now it happens that some people are interested in the welfare and high development of the human race; but leaving aside those exceptional people, all fathers and mothers are interested in the welfare of their own families. The dearest thing to the parental heart is to have the children marry well and rear a noble family. How short-sighted it is then for such a family to take into its midst a child whose pedigree is absolutely unknown; or, where, if it were partially known, the probabilities are strong that it would show poor and diseased stock, and that if a marriage should take place between that individual and any member of the family the offspring would be degenerates.[39]
In the 1970s, as adoption search and support organizations developed, there were challenges to the language in common use at the time. As books like Adoption Triangle by Sorosky, Pannor and Baran were published, and support groups formed like CUB (Concerned United Birthparents), a major shift from "natural parent" to "birthparent"[182][183] occurred. Along with the change in times and social attitudes came additional examination of the language used in adoption.