They stopped believing in God. They saw a disconnect between what Catholics say and what they do. They disagreed with the church’s stance on social issues such as homosexuality and birth control.

They are the growing numbers of young Catholics leaving the church — the focus of a new national study to examine why they’re departing and where they’re landing. It’s an issue that worries church leaders across the country.

“Leaving the [Catholic] church crosses all age groups, but the fastest growing demographic is age 18 to 29,” said John Vitek, president of Saint Mary’s Press in Winona, which commissioned the study.

“Our data shows the median age for leaving the church was 13 years old,” he said. “That was a surprise to everyone … and something we really have to take note of.”

Minnesota is home to more than 1 million Catholics, and the study is being read with interest by Catholic school teachers and church leaders.

Called “Going. Going. Gone: The Dynamics of Disaffiliation in Young Catholics,” the unusual survey focused on former Catholics between ages 15 and 25. It is based on a random sample survey of 204 teens and young adults, as well as 15 personal interviews. The research was conducted by the Center for Applied Research in the Apostolate (CARA) at Georgetown University.

Its findings were unveiled at a national conference in Baltimore earlier this year. Vitek is already slated to present findings in more than a dozen cities in the months ahead.

The survey found that the biggest reason young Catholics bailed was that they no longer believed in God. One in five cited that lack of faith.

“I would like to believe that something happens when you die, that you don’t just rot in the ground, but I don’t know,” said one young woman.

Another 16 percent said family experiences shaped their misgivings. Divorce, death, illnesses and perceived “hypocrisy” were cited.

“Although my grandparents took me to church every weekend … we found out that my grandfather was having an affair,” said another respondent. “I don’t think that’s part of the Catholic faith.”

Others were put off by the church’s stance on social issues such as same-sex marriage and the role of women.

“I believe in birth control. ... I am a complete supporter of same-sex marriage,” said one teen. “I’m fine with priests being married. This whole being married to Jesus or God thing is kind of ridiculous.”

Once they leave the church, more than a third report no religious affiliation and 29 percent switch to another Christian denomination.

Among other findings:

• Three in four said they stopped viewing themselves as Catholics between age 10 and 20.

• Nearly half said they were searching for spiritual practice in tune with their beliefs.

• About a third said they are “done” joining churches.

The findings sadden but don’t surprise religion teachers in Twin Cities Catholic schools.

“My reaction was, it’s about time we started listening to their stories,” said Becca Meagher, a religion teacher at Benilde-St. Margaret’s school in St. Louis Park. Only by understanding why can the church respond, she said.

“I’ve been teaching for 20 years and I’ve seen some of this in my classroom,” added Holly Hoey Germann, a religion teacher at Totino-Grace in Fridley. “It’s a reflection of the larger culture, which is not accepting of big institutions.”

But, she noted, “Doubt is a natural companion to faith.”

Saint Mary’s Press seems like an unlikely sponsor for such a study. It is best known as the publisher of Catholic textbooks and Bibles, with sales of about 500,000 a year.

The study already is informing the next batch of texts, Vitek said. New textbooks will include “opportunities for young people to question and wrestle with their doubts,” he said.

There will be “reflective questions” next to text allowing readers to express and explore their personal experiences, he said.

Meanwhile, public interest in the research continues to grow, said Vitek, with more than 15,000 copies ordered so far. Last week, one bishop ordered a copy for every priest in his diocese, he said.

“It’s quickly having an impact,” Vitek said.