Gay couples are more heavily criticised than their straight counterparts over parenting.

Researchers at the Binghamton University in New York found that people are prejudiced against same-sex parents.

The team looked at people's reactions to the parenting behaviours of gay and straight couples and found a pattern of negative reactions towards same-sex participants, despite them engaging in exactly the same parenting behaviours as the straight couples.

Sean Massey, one of the study authors, said: "We noted that when parents displayed favourable parenting behaviours like comforting an upset child, gay and straight parents were judged in a similar, positive manner.

"However, if parents got frustrated - raised their voice or slapped their child on the hand, the gay parents were judged more negatively than the straight parents."

The researchers believe gay parents are held to a different standard to straight parents, and that this has wider implications when it comes to same-sex couples adopting or fostering children.

At present, there is a shortage of people adopting and fostering children and the gay community is a huge resource that should be used to help these children, the researchers say.

However, the study indicates that gay parents are being placed at a disadvantage because of prejudicial attitudes held towards them.

"We feel that it is very important for social workers and adoption counsellors to be made aware of the effects of modern anti-gay prejudices and they need to educate themselves and develop policies that help protect against these potential biases," said Massey.

Lesbian couple
Researchers say study shows prejudices against same-sex parents (Reuters)

"Raising awareness of these attitudes is a critical step in being able to utilise a potentially valuable pool of prospective adoptive and foster parents, but it is also vital to improving the day to day lives of our families and our children."

"Prejudicial judgments, however subtle, that serve to limit access of these families to potential support and resources, ultimately harm today's youths."

The US Supreme Court is today hearing arguments about the law surrounding gay marriage.

A recent Washington Post/ABC News poll found that 58 percent of Americans favour the right to government-sanctioned marriage for gays and lesbians, with 36 percent opposed.

Lawyers representing a gay couple from California will try to convince the court to quash the state approved ban on same-sex marriage and allow same-sex couples to marry nationwide.

Jennifer Levi, professor of law at Western New England University, said: "People have seen there has been no negative impact (from gay marriage). It's only the exclusion from marriage that has a negative impact."

However, despite widespread support, many people are still opposed to allowing gay couples to marry.

Brian Brown, who is one of the nation's leading opponents to same sex marriage, said: "We remain confident that the US Supreme Court will uphold the ability of states and the federal government to define marriage as the union of a man and a woman, a definition that has served our nation well for hundreds of years."