On a hot July day in 2013, singer Sydney Sierota and her three brothers are doing their best to entertain a small group of fans at PNC Music Pavilion. Dressed in red shorts and a black T-shirt with the sleeves cut off, Sierota exudes a bit of shyness as her band, Echosmith, cruises through a brief set on a mobile trailer stage, on the Vans Warped Tour grounds, far away from the main stages. She had spent the day trying to coax fans to check out their set, and those in attendance appear impressed with the family pop-rock band.

Fast forward to the 2014 Vans Warped Tour where Echosmith, this time around, is performing under cover of the amphitheater to a packed crowd that's singing along to all of the band's songs. Sierota appears to have overcome her shyness as she perches at the front of the stage and urges fans to sing or dance along, shaking a tambourine and basking in the lights.

The dichotomy between performances is the easiest way to chart the band's growth. Add to that their first U.S. headlining tour, which stops at the Visulite Theatre on Feb. 25, and it's plain to see the band's upward trajectory continues.

"Growing is always good news," Sierota says recently by phone before appearing with her band on Good Day L.A. "You always hope that when you go back on tour, it's slightly bigger the next year. If you're staying in the same spot or demoted, it's not a great sign. It was exciting to see things grow in a real way."

Warped Tour has become a bootcamp and proving ground for countless artists. Young bands get a crash course in self-promotion by walking around and telling people to check out their performance. Bands perform under harsh mid-summer parking lot conditions on stages of all sizes. Do well, you'll be invited back or better ­— hit the road on a headlining tour. Fail to impress and chances are most people won't see your band ever again.

"It was intimidating, especially the first year," Sierota, 17, says. "We were so different [from the other bands], we didn't know if anyone would like us. We found out pretty quickly that people did like us though, which was cool. Warped Tour helped me become a lot more comfortable talking to anybody now. It helped me to grow up pretty fast."

It also helped the family — Sydney is joined by her brothers, 21-year-old guitarist Jamie, 19-year-old bassist Noah and 16-year-old drummer Graham — work on their communication skills with each other. When you're in a family band, there's really no where to run when things get tough. Especially when your parents are on the road with you, too.

"You learn how to communicate and work things out instead of giving up," Sierota says. "We know how to get along and have fun — sometimes we forget, of course — but a lot of siblings don't ever get to have something like this. [Touring with family] is nice because it's five less people to miss. I get to see them every day."

The family never intended on forming a band. Sure, dad's a music teacher and songwriter and mom's a painter, so there's no doubt they would be artistic. When they picked up instruments, it was simply what they were interested in. When they heard someone needed a young, and free, band to play a charity event, it just so happened they had all picked the right instruments to facilitate a band. That was back in 2009.

These days, Echosmith is riding on the strength of their own songs ­— infectious indie-pop tunes that teens find easy to relate to. The band's single, "Cool Kids," has gone platinum and charted around the world.

Warped Tour promotion might have helped with that a bit. The band was handing out free CD samplers to get their music into as many people's hands as possible. As time went by over the course of the summer ­— and from year to year, Sierota noticed more and more people singing along to the song while they were performing it.

They've now performed that song and others on plenty of TV shows — from Ellen and the Today Show to Jimmy Fallon and Conan ­— and have opened for bands including Neon Trees and American Authors.

"We always continue to be ourselves," Sierota says. "I remember what it was like to play for 100 people after I begged all of them to be there. Here we are now playing shows where people are choosing to be there. [Warped Tour] had a great impact on what we're doing these days and how grateful we are that we get to do this."