When the Big Easy calls, a true jazzman cannot refuse - even if he's in the throes of diaper changes and midnight feedings of his 2-week-old, first-born daughter.

With North Penn High School's award-winning Navy Jazz Band slated to perform at the venerated New Orleans Jazz and Heritage Festival this week, on a main stage - a first-ever honor for a school ensemble from outside the Crescent City - band director David DiValentino knew he had to put paternity leave on hold.

His wife, he said, commanded him to "Go! . . . This is a once-in-a-lifetime thing."

There was no need to point that out to the 23 band members, who will share the festival program with the likes of Paul Simon, Pearl Jam, and the jazz-fusion jam band Snarky Puppy, a favorite of the budding musicians from central Montgomery County.

The group, which flew south Wednesday, will play a 50- to 60-minute set on the WWOZ Contemporary Jazz Stage at 11:15 Thursday morning. The festival, with hundreds of acts drawing about a half-million visitors, runs through Sunday.

The North Penn Navy Jazz Band (navy referring to the school's color) is accustomed to regional acclaim, but the chance to play its hit list - from Count Basie's "April in Paris" to Blood, Sweat and Tears' "Spinning Wheel" - in the birthplace of jazz was undreamed of.

"I knew we were really good," said trumpet player Josh Faia, 18, a senior. Still, when he found out about the invitation, "I didn't believe it. ...

"This thing we've been trying to emulate all these years, we're going to the original."

The band's big break came through hard work, with a dash of Cajun-spiced luck.

When the North Penn players won the regional SteelStacks High School Band Jazz Showcase in Bethlehem, Pa., last spring - an honor they grabbed again this year - they earned a gig at that city's Riverfest, opening for New Orleans' renowned Dirty Dozen Brass Band. They caught the ear of its trumpeter and leader, Gregory Davis, who also books acts for the Jazz and Heritage Festival.

"I was impressed with their musicianship, the phrasing, the level of improvisation," Davis said. "You could tell something was going on in the school. So that prompted me to get them here for Jazz Fest."

DiValentino recalls Davis' telling him that the North Penn kids - who practice twice a week in two-hour sessions after school - "had a really mature sound."

When Davis called last August with the official invitation, it triggered a flurry of fund-raising to help defray the cost of flying the large group to New Orleans and staying five nights. The students, 15 parents, and five school staffers still are paying about $600 each for the odyssey.

The band's sole female is bass player Emma Sweeney, 18, a senior whose story echoes the North Penn ensemble's can-do refrain.

When she decided to learn the bass in third grade, she had no idea what an unusual choice it was.

"I liked the sound and nobody was picking it, so I thought, why not? Little did I know there were no girl players," recalled Sweeney, who also is a member of North Penn's orchestra, string quartet, and chamber ensemble.

Her hero is Esperanza Spalding, one of the few female jazz bassists. Sweeney knows only one other girl bass player: her little sister, who was inspired by her older sibling.

Sweeney recently won a full scholarship to study neuroscience at Temple University. But two other band mates are headed to the Berklee College of Music in Boston next year.

The student musicians credit DiValentino, 34, who took the helm last year and sometimes plays trumpet with the Philly Pops, with getting them this far.

The New Orleans Jazz Fest, which dates back to 1970, has always made an effort to spotlight school bands - though usually local ones like the New Orleans Center for the Creative Arts, the legendary institution that schooled Wynton and Branford Marsalis and Harry Connick Jr.

"I think it's really cool that we're the first high school from outside of New Orleans that gets to do this," said trumpeter Josh Weckerly, 17, a senior. "Our jazz program has come a long way since Mr. DiVal has taken over."

For the director, the prestigious gig means going straight from one happy daze - those late-night feedings of his new daughter, Lia - into another.

"Needless to say, I'm enjoying life right now," he said. "It is definitely a year to remember."