Harmonized voices sounded from within choir director Michael Horanski’s classroom at Robinson Secondary School in Fairfax.

The school year might be waning, but Horanski’s students were gearing up for a summer of hard-fought competition at the World Choir Games, the toughest challenge they have faced.

The choral competition promises to host as many as 15,000 singers from about 360 groups from 60 countries.

“We had to send an audition recording for their review. Music had to be approved by an artistic committee in December,” Horanski said.

Although entering the competition has meant more work for students and their director, he said the payoff is clear.

“The process that we’re going through, it makes the students put an added investment into choir,” Horanski said.

Horanski began eyeing the World Choir Games more than a year ago, when the competition organizers, Interkultur — a German-based nonprofit group that organizes music competitions — announced their plans to host the first games in North America. The event is staged every two years and will be July 4-14 in Cincinnati.

“We’ve been working . . . all year, trying to get everything down perfect,” said senior Dan Bonilla, 17. “We’re pretty much just fine-tuning now. . . . The choir that wins the best overall, pretty much the gold medal, is basically the best choir in the world.”

Two Robinson choir groups, the high school level Robinson Singers and Select Women’s groups, will compete. Overall, 59 Robinson students will travel to Cincinnati.

Junior Molly Johnson, 17, is competing with both groups.

“It’s the first time [the World Choir Games] has been in the U.S., so that’s the only reason we can afford to go,” she said. “We’ve been fundraising like crazy. Tons of car washes, bake sales. We’ve been paying fees since August.”

The per-student cost was about $850 before fundraising. Additionally, the teams paid $250 each as a registration fee.

Students will travel to Cincinnati by bus and participate in the opening ceremony July 4. There are two competitions within the World Choir Games: the champions competition, in which choirs that meet certain qualification standards will compete, and the open competition, which is for any choir at any level. Choirs are divided into 23 categories, based on age, composition of the group — for example, all male or female ensembles —and style of music performed.

“This is a choir that we really have an interest in,” said Lori Lobsiger, Interkultur’s director of North American markets.

She said Horanski and his students were a standout among the groups who had to submit performance demos to qualify for the competition. Lobsiger said she expected Robinson to perform well during the games and to qualify for the champions competition.

“You’re not really competing against one another at all. It’s more of you coming in and doing your best,” she said.

The competition is judged by an international panel of experts.

“The judges are either highly recognized directors . . . composers” or academics such as university music directors, Lobsiger said.

The World Choir Games is expected to draw a crowd of 100,000 to 200,000 visitors and generate an estimated $73.5 million for businesses in Cincinnati. The city competed with others worldwide to win the bid for the World Choir Games. It won out because of its availability of music venues, cultural history and workability, said Dan Lincoln, director of the 2012 World Choir Games and president and chief executive of the Cincinnati USA Convention and Visitors Bureau.

“Typically, as a Midwestern city, you don’t think of yourself being on a world stage. We’ll never see ourselves the same way again,” Lincoln said of the size and importance of the World Choir Games.

Organizers compare the games to the Olympics, saying the event carries the same pomp and circumstance as well as quality of entertainment.

“It’s the World Choir Games, so it’s going to be music from all over the world,” said Robinson junior Maya Davis, 16. “We have no idea what to expect.”

Senior Zachary Miller, 17, who said he wants to be a music educator, said: “It gives us a chance to see other world cultures and be able to see that ‘hey, we’re not the only ones out there.’ You don’t need to speak [another language such as] Spanish to understand the emotions that come to people in a piece. It’s not every day that you get to sing with people from other countries. . . . It’s a pretty big deal.”

There will be an end-of-the-year concert at 7 p.m. next Thursday at Robinson Secondary School. The concert is one of the last chances for students to perform publically before the World Choir Games.

“It’s a really good way to sum up our high school careers. [Choir] has been a huge part of our last four years,” senior Paige Brindley, 18, said.