Pulling off a day-long conference for more than 3,000 participants is tough — especially when you’re a teen.

‘‘The culture would say that teenage and adolescent years are foolish years and years of immaturity,” said 17-year-old Kristin Hoover of Gaithersburg. ‘‘We’re going to come up to that challenge and say ‘No, that’s not OK with us. We’re going to live these years.”

Hoover, a Covenant Life Youth Group member who served as a conference leader, said American culture promotes an ‘‘If it feels good, do it” attitude, but the teenage years are pivotal. ‘‘They are the formative years of who you are going to be for the rest of your life.”

Gaithersburg was the last stop on a seven-city book tour for Alex and Brett Harris, 19-year-old authors of ‘‘Do Hard Things: A Teenage Rebellion Against Low Expectations.”

More than 3,200 teens, ‘tweens, and parents gathered at Covenant Life to hear the twins from Gresham, Ore., speak of ‘‘grace,” their love for Christ and using their God-given potential to make tough choices to advance goodness.

Some of those who attended came from far-flung cities, including Englewood, Calif., and Rochester, N.Y. Some came from as far away as Kenya, Germany and Great Britain.

‘‘It’s not because we’re anything special – it’s because God is still using the youth to spread the Word and he wants to use you,” Brett Harris told his audience, highlighting a blog the brothers started that received 18 million hits last year and their book, which brought six publishing offers. At 16, the home-schooled brothers received a personal invitation to apply for internships at the Supreme Court of Alabama – jobs usually enjoyed by law school students, Harris said. The brothers got the coveted positions.

‘‘We’re just two guys who started a blog. We’re just two sinners saved by God’s grace. ... We’re just two teenagers willing to do hard things,” Brett Harris said, citing a list of history’s successful teens, including George Washington and Clara Barton, founder of the American Red Cross, and society’s current ‘‘low expectations” of American youth.

(They are also just the brothers of Joshua Harris, 33, senior pastor of Covenant Life and five-time best-selling Christian author, and the sons of Gregg Harris, who pioneered the Christian home-schooling movement, penned a best-seller and has led nearly 200,000 families in seminars.)

Teens scribbled notes, bought books and had their T-shirts signed at Saturday’s conference. They swayed and danced to a Christian band. Some stood to be ‘‘saved” at an altar call during worship.

Casey Somerville, 21, referred to the Rebelution as ‘‘making wise choices and living for God’s glory.” As Covenant Life’s youth secretary, she helps coordinate monthly meetings for about 500 youth group members and parents and smaller discussion groups. Born-again Christians follow a literal interpretation of the Bible, Somerville said. Teens can ‘‘be a light for Christ,” abstaining from sex outside marriage or drinking and ‘‘do hard things” in big and small ways.

The Rebelution calls teens ‘‘to look for areas in your life where you’re just accepting the culture’s values...and saying ‘How does God think about this?’” Hoover said. She mentioned ‘‘the modesty movement,” asking young women not to ‘‘flaunt their body.”

‘‘A big obstacle for me is that I’m losing my vision,” said Joanna Linn, 16, of Gaithersburg, a youth group member. The challenge has strengthened her faith and she will spread God’s Word ‘‘however he wants to use me,” she said. ‘‘I can’t convert anyone, but I can show God’s love.”

Brett Jansen, 17, of Gaithersburg felt called Saturday to raise money to build wells in Africa, he said. Two of his siblings went on a two-week mission and said there was a need.

Conner Burk, 12, of Crozet, Va., said the day encouraged him to think of ‘‘big things” to help halt homelessness and poverty, problems just coming to his attention.