Smith, director of the Chapel Hill High School Orchestra, stood on a small riser in the center of the stage in the band auditorium and faced the students arrayed in a semicircle around her. The violinists played an up-tempo tune in time with her staccato baton beats.

"Two, three, four . . . cellos!" she called, and the cellos dove in.

She wore a black T-shirt that read "Orchestra Rocks!"

Friday night it sure will. More than 300 string musicians from the orchestras of the three high schools and four middle schools in the Chapel Hill-Carrboro School District will take the stage together for the annual All-City Orchestra Concert.

And this will be no ordinary string concert. Mark Wood, an internationally known musician as a member of the Trans-Siberian Orchestra and an influential music educator, will be in town to lead the performance -- and where Wood goes, rock follows.

In his performing and his teaching, he introduces rock styles and techniques -- jamming, improvisation, driving beats and so on -- into students trained in classical music.

When's the last time you attended a string orchestra concert and heard "Stairway to Heaven"? You will on Friday. The show is being billed as a "rock-estra."

"Our kids are taught almost exclusively classical music," said Smith, who directs the CHHS and Culbreth Middle School orchestras. "We might have a smidgen of jazz and a smidgen of bluegrass, but it's mainly classical. So this is a big change and an exciting one, for all of us, including me. Mark Wood has violins doing what the electric guitar does."

Wood, lead violinist and string conductor for the Trans-Siberian Orchestra, is also a board member of the American String Teachers Association. He travels widely teaching a program he developed called Electrify Your Strings. The idea is to update and re-focus the concept of music education in public schools by bridging the gap between classical and alternative music. This will be the first time the program has come to the Triangle.

The orchestras at the local schools -- Chapel Hill, East Chapel Hill and Carrboro high schools and Culbreth, McDougle, Phillips and Smith middle schools -- have rehearsed the concert program for weeks. Wood will conduct workshops with the middle school students on Thursday and the high school students on Friday, all leading up to the big show Friday night. The students will play along with Wood and members of the Trans-Siberian Orchestra.

It's going to be a big change of pace for many of the classically trained students.

"Everybody knows TSO, and this is a great, great opportunity to play with them," said bassist Shaan Hassan, president of the CHHS orchestra. "The orchestra crowd isn't exactly the rocker type, but I think this will open up a lot of people to some new music and new styles of playing."

Smith said much of Wood's approach is designed to help young musicians build their improvisational skills. That's something classical music doesn't typically emphasize, to put it mildly.

"Some kids just naturally know how to improvise," she said. "You can say, 'Pentatonic scale, A minor!' and they can just break out and go for it. Some others, like me, aren't used to that at all. The way I learned was, you read the music, you count the music, you play the music. This is a very different approach. I'm really happy this program is out there."

Smith met Wood and learned about his teaching program at a convention of the American String Teachers Association in Detroit. After doing some research and talking with other teachers who had brought him to their schools, she was sold. She set about writing grant proposals, coordinating dates and making arrangements.

"I can hardly wait," she said. "I've been losing sleep, thinking, 'Is everything ready? Have I gotten everything done?' But I think we'll be ready to go."

The program Friday will include works by groups including the Beatles and Led Zeppelin, as well as some of Wood's own compositions.

"A lot of the kids are really excited about it," said Jeremy Bellion, who directs the orchestra at Smith Middle School. "There are some students who really prefer classical music and have been a little more cautious. But even the kids with a more traditionally classical approach have been getting into it, and I think that once they get up there and have a chance to play and talk with Mark Wood, they're all going to have a great time.

"I'm really looking forward to it. It's going to be very, very eye-opening."