“If/Then” co-stars Idina Menzel, left, and Anthony Rapp rehearse in New York before the musical’s D.C. debut. (Matthew Murphy)

It’s true, as the song says, that if you make it there you’ll make it anywhere, but sometimes it’s best to take a first nibble somewhere besides the Big Apple. That’s the case with “If/Then,” a musical making its world premiere at the National Theatre before moving to Broadway next spring.

It’s the second time the show’s creative team has tested material in D.C. Tom Kitt, who wrote the music, Brian Yorkey, who wrote the script and lyrics, and director Michael Greif were all behind “Next to Normal,” which got a pre-Broadway workout in 2008 at Arena Stage. When the rock musical moved to the Great White Way in 2009, it earned 11 Tony nominations and three awards.

“I don’t want to say it’s superstition, but it worked before,” says Anthony Rapp, who reunites with “Rent” co-star Idina Menzel for “If/Then.” Rapp and Menzel, who won a Tony in 2004 for “Wicked,” share the stage with another big name: LaChanze, who nabbed a Tony in 2006 for “The Color Purple.”

The out-of-town tryout used to be standard; in fact, the National Theatre hosted the pre-Broadway engagement of “West Side Story,” in 1957. Both Rapp and Carmel Dean, “If/Then’s” music director, find the process immensely valuable.

“It’s so hard to know what you have until you have it in front of people, especially something new — this isn’t something based on anything else,” Rapp says. “Like a lab [experiment], it has to be hermetically sealed, to some extent, but you have to expose it to something to get it to react.”

LaChanze, left, and Anthony Rapp work out a scene during rehearsals for “If/Then” in New York. (Matthew Murphy) LaChanze, left, and Anthony Rapp work out a scene during rehearsals for “If/Then” in New York. (Matthew Murphy)

“It’s impossible to hit perfection the first time around,” Dean says. “There are so many facets that need to be explored and the audiences and the critics on Broadway have such high expectations. These musicals cost millions of dollars, and not to have a trial run is very risky.”

Another element unique to a new show is that the script is not set: The creative team is constantly making tweaks both small and large.

“Yesterday was the first time the actors have all been on the set,” Dean said on Oct. 24, less than two weeks before the show’s first scheduled performance. “So we’ll find out that, say, the actors need more time to walk up the staircase, so we need four more bars here.”

Not all changes are of the walking-up-stairs variety. “There was one moment when Tom and Brian were trying to write this song for this character and it just wasn’t working,” Rapp says. “They kept trying new things, and then they brought in this totally new song and everyone was like, ‘Yes!’ ”

“It might be a silly metaphor,” Rapp adds, “but when you fly something new up the flagpole and see how many people salute, that success is very evident.”

The Story

The minds behind “If/Then” are keeping its plot under wraps. We do know that the show follows Elizabeth (Idina Menzel), who moves back to New York City around the time she turns 40. The show splits into multiple timelines, each with its own consequences. Last time around, the team was just as careful about “Next to Normal,” which has a gut-punching twist.

National Theatre, 1321 Pennsylvania Ave. NW; through Dec. 8, see thenationaldc.com for times and prices; 202-628-6161. (Metro Center)