Flashy worship services meant to attract millennials and teens are doing the opposite—turning them off instead.

That surprising revelation emerged from a recent in-depth study of more than 250 congregations in the United States and published in the book "Growing Young: Six Essential Strategies to Help Young People Discover and Love Your Church," the Washington Post reports.

The book's authors say today's generation is not interested anymore in things that church leaders consider "cool"—like flashing lights and rock-band atmosphere—during Sunday services.

Instead, today's young people are eager to feel some "warmth" inside their churches—congregations that "welcoming, accepting, belonging, authentic, hospitable and caring."

Those were the words used by many of the more than 1,300 young churchgoers, ages 15 to 29, who were interviewed in the study when asked what kind of church they prefer.

In short, the book's authors—Kara Powell, Jake Mulder and Brad Griffin—say today's youth prefer "authenticity and connection" in choosing the church they want to belong to.

"Across the board in statistical analyses, this warmth cluster emerged as a stronger variable than any ministry program. Ironically, it is possible that your church might be working against warmth by offering myriad programs. Busyness doesn't equal warmth," the authors say.

The authors say that when they suggest that churches need to grow warmer, they don't mean that adult congregants should be nice to young people. "Nice does not cut it. And warmth is more than superficial community," they say. "It's 'like family' — as young people told us again and again during our interviews and field visits."

The authors shared some ideas on how as church can become a warmer community. Here are just three of them:

● Encourage worship among various generations. "Intergenerational relationships grow everyone young by breaking the silos of age- and stage-based ministry. Consider setting up mentorship pairings so teens and parent- or grandparent-aged people can learn from each other."

● Turn church into big family room. "Rather than lean into the allure of viewing the worship service like a trip to the theater, imagine it as a gathering in the family room. Whether you meet in a sanctuary filled with pews, a contemporary auditorium, a high school gymnasium or an actual house, envision your worship experience like a family room."

● Make tiny churches within the church. "While we can't tell you which small group format will work best for your community, we encourage you to consider how what you're doing fuels warmth through peer friendships and intergenerational connections."