The group was chosen to sing with the Rolling Stones when they perform next week in Philadelphia.
"At first I didn't know if it was a bit of a joke because it's outside of the realm of what we normally do. I was tremendously excited, really excited," said choir member Daniel Spratlen.
"I've been a Rolling Stones my whole life," said accompanist John Grecia. "Half my life is classical music, the other part is performing rock and roll music. So it's the perfect melding of those two worlds."
"I think choral music is really cool, but this is the coolest thing we've ever done. The coolest collaboration by far," said choir member Jennah Delp.
In every city on the '50 and Counting' tour, the Stones have a local choir perform with them during the song 'You Can't Always Get What You Want.'
Philadelphia is the 10th city. The shows are Tuesday and Friday next week.
"It's kind of a neat thing they used all these different choirs," said The Crossing Choir's director, Donald Nally.
This is actually a really busy time for the choir. It's the month of moderns. They have 3 concerts in 3 weeks, but they said there was no question about making time for this one.
"I wasn't sure, ya know. I said, 'You guys wanna do this?' They were like, 'Why are you asking me? Of course!'"
It's the opportunity of a lifetime, one these singers say they're sure they'll remember for a long, long time.