In a visit to Concord High School yesterday, Republican presidential candidate Mitt Romney shared the story of how he and his wife met as high school students and offered his views on fighting terrorists. He took questions on immigration and the possibility of a military draft, receiving polite applause from the several hundred students assembled in the school's auditorium.

The one note of discord came when a teacher told Romney she was insulted by his opposition to gay marriage.

"The comment you made kind of invalidates my family," said Cynthia Fish, a substitute teacher who lives in Concord with her partner of four years and her two young daughters.

The confrontation came just after Romney explained that he viewed marriage as "primarily an institution for the development and nurture of children." While he said he wouldn't prevent gay couples from entering spousal contracts if they choose to live together, "the government benefits of marriage I'd reserve for a man and a woman."

Romney congratulated Fish for her family, but he offered no apology for his belief that the purpose of marriage was for a man and a woman to raise children.

"That's certainly within your right, and people can live their life as they choose, and, you know, children can bring a great sense of joy," Romney said.

Romney pointed out that many children live in families with divorced or single parents, though it is not the ideal scenario.

"That's not to say these other forms aren't valid. But, for instance, we don't say a single person is married, even if they are raising children," Romney said. "I believe, in society, we want to bring a man and woman together."

It was a brief exchange in an hour-long discussion, in which Romney told stories that ranged from the personal to the biblical. In discussing the threat posed by "radical Islamists," Romney alluded to the tale of Cain and Abel.

"From the beginning, it's been suggested that there's evil in the world," he said.

He recommended a combination of military and diplomatic solutions to fight terrorists, working with countries with moderate Islamic governments to counter the influence of extremists.

"It's something in our world; it's evil," Romney said. "That's the world you're in - we're all in."

He also shared a story about his son's Boy Scout troupe sending an American flag on the Challenger shuttle that exploded mid-flight in 1986. Included in the crew of that shuttle was Christa McAuliffe, a former teacher at Concord High School whose portrait hangs just outside the auditorium where Romney spoke. The flag, which Romney managed to see months later, was recovered from the wreckage of the explosion.

"For me, it was like electricity went through my arm when I touched it, because it represented the sacrifices made by those patriots," he said.

Fresh off Tuesday night's debate against the nine other Republican presidential candidates, Romney avoided direct criticism of his rivals.

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