Libby Tofig was emoting her heart out as she belted a song of pain and rejection called "Still Hurting," when the music teacher interrupted.

"You have a really wonderful set of pipes," she said. But she told Tofig to tone down the emotion and simplify her delivery. Instead of putting her pain out there for everyone to see, think of something sad in her own life and let the feelings seep through.

"Put yourself emotionally in that very painful place," said Lea Salonga, looking chic in black pants, leather jacket and purple scarf.

For some people, having a Tony Award-winning Broadway star dissect your singing might constitute a painful experience. But like the pro that she hopes to be someday, Tofig started over and nailed the song.

The 1,200 or so in the audience at Council Rock South High School exploded in applause and cheers for the elated 17-year-old junior.

"Gorgeous voice," added Salonga, who was just 17 herself when she was plucked 25 years ago to play the lead in Miss Saigon, a Madame Butterfly-inspired tale of a doomed romance involving an Asian woman abandoned by her American lover. The Filipina actress went on to win Olivier, Tony, Drama Desk, Outer Critics, and Theatre World Awards, and was the first Asian to star in the Broadway warhorse Les Miserables.

For this crowd of sixth to 12th graders, however, Salonga is probably better known for her work as a princess - a Disney princess. She provided the singing voices for Mulan in the movie of the same name and Jasmine in Aladdin.

The chance to sing for - and, for a lucky few, with - the petite actress originated with an offhand remark. A few months ago, choir director Corey Axler showed students a video of Salonga singing "I Dreamed a Dream" from Les Miserables and gushed about how great she was when, a student suggested he invite her to Council Rock South.

"I thought, no way was that going to happen," said Axler.

But he found her agent and extended the invitation, and two days later the agent said he thought it could work. She was paid $10,000 for her appearance. Tickets for Council Rock students were $10; $12 for others.

"She's one of the greatest voices of our generation," said Axler, still gushing, who put together a program that mixed Salonga's singing and answering questions from students with a "master class" for six lucky young singers.

"I wanted her to hear the great singers at Council Rock and for the students to get some feedback," he said.

Besides Tofig, performers included sixth graders Cameron Flurry and Lucas Nunez, freshman Kate Fahey, sophomore Emily Goulazian, and senior Noah Barson, who got the once-in-a-lifetime chance to sing the crowd-pleasing duet from Aladdin, "A Whole New World," with Princess Jasmine herself.

"I've been singing it for most of my life," the 18-year-old theater kid said last week. "I've loved Aladdin for most of my life.

Before Barson's big number, Salonga heard Flurry, who recently appeared in Mary Poppins at the Walnut Street Theatre and received final callbacks for Annie and Matilda, sing "To Play This Part" from Ruthless.

"Oh, my God, you're amazing. I honestly don't know what to tell you," said Salonga, before assuring the girl that it was only a matter of time until she made it to the Great White Way.

Next was Nunez, a chatty sixth grader who sang "Where Is Love" from Oliver. He chose the song, he said, because he saw Salonga sing it in a YouTube video and because his mother liked it.

"You sound really nervous," she said gently, then instructed Nunez to look at the exit sign and not the audience.

And even though the song is about a boy longing for his mother, Salonga told him to think of someone he missed. Nunez said his grandfather died not long ago.

"You have to make it personal for you," she said.

Kate Fahey's take on "Astonishing" from Little Women was ... astonishing. Again, Salonga had very little to add to improve the performance.

The South Vocal Ensemble then sang a soulful rendition of the Beatles song "Blackbird," getting the ultimate praise from the singer: "That sounds like something out of Glee."

Then Salonga sang it with them. "I need to recover from that," Axler said after. "Oh, my God, that was so much fun."

Emily Goulazian was a standout with "I'm Not Afraid of Anything" from Songs for a New World, which she said her school was performing.

Then it was time for the duet.

Barson, wearing a blue shirt with rolled-up sleeves, a vest, and a pair of dark khakis, started off looking a little nervous. But when Salonga's beautiful soprano joined in, he looked as happy as Aladdin on his magic carpet.

"I was thinking a little bit, 'This is really awesome'; a little bit, 'Please, God, don't mess up'; and a little bit, 'I'm singing with Lea Salonga,'" he said when he was finished.

After answering some questions and warning students that anyone considering a theater career "should be honest about what they can and cannot do," Salonga stayed on stage to take pictures and sign autographs.

"These kids are excellent," she said, as the group of singers basked in the glow of a Broadway star. "I was really impressed."

kboccella@phillynews.com

610-313-8232

@kathyboccella