New York ? Adoptive parents invest more time and financial resources in their children than biological parents, according to a new national study challenging arguments that have been used to oppose same-sex marriage and gay adoption.

The study, published in the new issue of the American Sociological Review, found that couples who adopt spend more money on their children and invest more time on such activities as reading to them, eating together and talking with them about their problems.

“One of the reasons adoptive parents invest more is that they really want children, and they go to extraordinary means to have them,” Indiana University sociologist Brian Powell, one of the study’s three co-authors, said in a telephone interview Monday.

“Adoptive parents face a culture where, to many other people, adoption is not real parenthood,” Powell said. “What they’re trying to do is compensate. : They recognize the barriers they face, and it sets the stage for them to be better parents.”

Powell and his colleagues examined data from 13,000 households with first-graders in the family. The data was part of a detailed survey called the Early Childhood Longitudinal Study, sponsored by the U.S. Department of Education and other agencies.

The researchers said 161 families in the survey were headed by two adoptive parents, and they rated better overall than families with biological parents on an array of criteria – including assistance with homework, parental involvement in school, exposure to cultural activities and family attendance at religious services. The only category in which adoptive parents fared worse was the frequency of talking with parents of other children.

The researchers noted that adoptive couples, in general, were older and wealthier than biological parents, but said the adoptive parents still had an advantage – albeit smaller – when the data was reanalyzed to account for income inequality.

In particular, the researchers said, adoptive parents had a pronounced edge over single-parent and stepparent families.

The researchers said their findings call into question the long-standing argument that children are best off with their biological parents. Such arguments were included in state Supreme Court rulings last year in New York and Washington that upheld laws against same-sex marriage.