Fatherhood has been exhilarating for Weston Clark, who put aside a teaching career to be a stay-at-home dad for a 4-year-old son and 17-month-old daughter adopted by him and his husband.

Yet Clark acknowledged some unease as he looks ahead to late August, when his son starts kindergarten in Salt Lake City.

"How is that going to play out for him, the fact that he has two dads?" Clark wondered.

"The fact that his parents made a decision that already makes him stand out makes me nervous — that wasn’t his choice," Clark said. "We will fight in every way we can to make sure he’s OK."

The mix of pride, joy and apprehension conveyed by Clark is familiar to many parents — including many in America’s growing ranks of gay dads.

More so than heterosexual couples or lesbians, who can bear their own children, gay men face high hurdles en route to parenthood. The two main avenues open to them — adoption or surrogacy — can be costly and complicated.

"They have to go out of their way to become fathers," said Nancy Mezey, a sociology professor at Monmouth University in West Long Branch, New Jersey, who has studied gay parents.

By the tens of thousands, gay men are choosing to do just that. And as they celebrate Father’s Day this year, they can anticipate that their ranks will continue to swell if the U.S. Supreme Court, in a ruling due later this month, legalizes same-sex marriage nationwide.

A decade ago, it was far more common for lesbians to be raising children than for gay men. The gap remains but is closing.

Gary Gates, an expert on gay and lesbian demography with the UCLA School of Law’s Williams Institute, estimates that there are about 40,000 gay male couples in the U.S. who are raising children, and roughly three times as many lesbian couples who are doing so.

How are the gay dads doing? At this point, there’s relatively little long-term research comparing outcomes of children raised by gay fathers to the outcomes of other children.

Among the handful of scholars who’ve broached the subject is Abbie Goldberg, a psychology professor at Clark University in Worcester, Massachusetts.

On the one hand, she believes children of gay dads and lesbian moms will be less susceptible to gender stereotypes than children raised by straight parents. However, Goldberg says it’s possible that future research will reflect the challenges faced by the many gay dads who have adopted their children. On average, adopted children have higher rates of health and behavioral problems than other children, according to the research group Child Trends.

Comparing lesbians or straight families with biological kids to gay men with adopted kids "could in theory make gay dads look worse," Goldberg said.

But Goldberg said gay dads tend to have higher incomes than lesbian moms, and also tend to have good relations with the birth mothers of their adopted children. "They’re more OK with granting birth moms a special role in the family," she said. "They don’t feel their role as parents is threatened."

In Philadelphia, Greg Girdy and Paul Yorgey keep in contact with the birth mother of their adopted 4-year-old daughter, Bella. The mom attended a recent party celebrating Bella’s baptism.

The dads also can call on a host of other women in their extended families to serve as female role models. Yet they sometimes bridle at unsolicited advice.

"As two men, when we adopted, a lot of people think we need help, in a way that would never happen for a straight couple," Girdy said. "Like Bella’s hair care, or what clothes she should wear. … We tend to get advice when we don’t need it or want it."

In addition to Bella, the Girdy/Yorgey household includes two boys from the local foster-care system. The men expect to adopt a 7-month-old once some logistical matters are resolved, while the other boy, who’s nearly 5, may be returned soon to his mother.

"That’s one of the stresses we face," said Girdy, a lawyer. "We’re two non-biological dads. Any time possible, the family court wants to reunify that kid with the mom, even if the mom shows no connection with the kid."

Girdy and Yorgey have been a couple for 11 years, and married in March 2014, the same month that Bella’s adoption was completed. They had been talking about having kids since early in their relationship, but once they started the adoption process, it took four years before Bella joined the family.

The dads are a study in diversity. Girdy, a 45-year-old African-American, grew up in Texas, and still roots avidly for the football team of the University of Texas, his alma mater. Yorgey, 30, grew up in the Philadelphia suburbs, part of an Irish-Polish family devoted to the NFL’s Eagles.

"When we were dating, we never referred to ourselves as a gay couple," Girdy said. "But once we did adopt, we needed to show Bella we are proud of who we are, so when someone asks her who her parents are, she can proudly say, ‘I have two dads.’"

A similar brand of family pride has been on display at the U.S. Capitol since Rep. Jared Polis, a Colorado Democrat, and his partner, Marlon Reis, became dads. They have a 3½-year-old son, Caspian, and a 1-year-old daughter, Cora.

Polis said he and Reis face the same challenges as other parents — "There’s no gay way or straight way to change diapers in the middle of the night."

However, he hopes his family might have some influence on House colleagues who have opposed legal recognition of same-sex couples. "Even the most conservative Republicans like to hold Cora or talk to Caspian when I bring them on the floor of the House," Polis said.

In Salt Lake City, Weston Clark and Brandon Mark also are feeling welcomed as they settle in to married life and child-rearing.

Clark, 36, and Mark, 37, have been a couple for 15 years, and adopted their son, Xander, in 2010 when there seemed to be no foreseeable prospect of same-sex marriage becoming legal in Utah. At the time, Utah law even blocked gay couples from adopting, so the two men established residency in California and completed the adoption there.

On Dec. 20, 2013, as they were in the process of adopting their second child, change came suddenly. U.S. District Judge Robert Shelby, in a ruling that was soon echoed in numerous other states, struck down Utah’s ban on same-sex marriage.

Clark, who received a text message with the news, was excited yet worried that the opportunity to wed might be brief. He called Mark at work with a question, "Do you want to go get married?"

"We wanted to get it done in the window," Clark said. "We had our kids. We wanted protection for them."

While firing off text messages to friends and family, the men rushed to the county clerk’s office late in the afternoon.

"It was just chaos," Clark recalled. "We got there at 4:45. We got married by the mayor, on live TV."

Looking back, Clark says the decision to raise children — made in 2010 — was even more momentous for him and Mark than the decision to get married.

"We asked ourselves many times: Do we really want to do this? Is it good for us as a couple? Is it good for the child to bring them into that environment?" Clark said.

"There’s no question that having a child has been beneficial to me and our relationship," Clark added. "We had given thought from the beginning to whether having these kids would be good for them in the long run … So far it’s been amazing."

One of the couple’s key decisions involved the division of work and family responsibilities. Mark works for a Salt Lake City law firm, while Clark, a former high school teacher, says he’s happy as a stay-at-home dad.

Mezey, the Monmouth University sociologist, says the initial division of work/family responsibilities can be challenging for some pairs of gay dads. But she says there’s research suggesting that those who decide to stay at home with the kids are often pleased at the results. "They challenge dominant beliefs that dads are primarily breadwinners and can’t be the primary nurturers," Mezey said.

Overall, Mezey believes gay fathers can carve out a distinctive niche for themselves.

"They’re adopting children that other people don’t want to adopt. They’re teaching their children tolerance and expanding definitions of gender roles," she said. "They are helping to redefine what it means to be a real man."