Benjamin Zander, one of Boston’s most prominent classical music figures, is back leading a youth orchestra. Watching him now, one could find it hard to imagine that less than a year ago, his four-plus decades at New England Conservatory came to an ugly end.

No rehearsal begins without a speech: “We all love NEC,” he tells the more than 100 musicians, ranging from 12 to 22 years old, members of the newly formed Boston Philharmonic Youth Orchestra, on a recent Saturday afternoon. “The tension is over.”

By tension, Zander means the fallout from his hiring a registered sex offender to film concerts and rehearsals with NEC’s top youth orchestra in recent years without telling school administrators. The videographer was not accused of any wrongdoing at NEC, but Zander’s failure to tell the administration about the man’s history led to Zander’s firing last January.

“I call it a bump, a serious bump in the road,” Zander said. “Now, I’ve got a chance to really think through, at every level, what it is I want . . . Shaping future leaders through music. That’s my life work.”

For most anybody else, building a 117-member youth orchestra from scratch would seem impossible. But the Boston Philharmonic Youth Orchestra will debut Nov. 25, in Symphony Hall, with star cellist Alisa Weilerstein as soloist. This is a long way from last winter, when Zander’s dismissal sparked student protests and an online petition on his behalf signed by more than 1,200 people, including Pulitzer Prize-winning composer John Harbison, Boston Musicians’ Association president Pat Hollenbeck, and Harvard scholar Christoph Wolff.

Almost immediately, friends, former players, and students in his NEC orchestra urged Zander to start his own youth ensemble. He resisted, unsure of his next step, though he continued as music director and conductor of the Boston Philharmonic Orchestra. Eventually, the Philharmonic’s leaders and friends convinced him.

“It wasn’t just getting Ben through a personal crisis,” says Mark Churchill, the former NEC dean who has been a key Philharmonic Youth Orchestra organizer. “It was about giving young people the opportunity to work and to study music and have this experience with Ben that was so significant. There were the immediate kids who sort of felt cut off at the knees when he left. They wanted to continue.”

Even at the new orchestra’s first auditions, in May, Zander wasn’t sure he really wanted to go forward.

“I felt pretty beaten up, and I’m 73, and the idea of starting a new institution was a little daunting,” Zander said. “When the students started coming in, then it became really exciting.”

For some of the young musicians, the decision to join the new orchestra wasn’t easy. There are a number of long-established youth orchestras in Boston, including the highly competitive NEC Youth Philharmonic Orchestra, which Zander had led, and the Boston Youth Symphony, which is in residence at Boston University.

Those top orchestras perform in Jordan Hall and Symphony Hall and have firmly established infrastructures. Posts appeared on Facebook earlier this year as young players debated which ensemble to audition for.

“It was scary,” said Joe Blumberg, 15, a trumpet player who had been in NEC’s top orchestra. “The first time I saw the [new orchestra’s] website it said they were playing ‘Ein Heldenleben,’ and I was scared that he could get that many people to make it happen. But I knew that Mr. Zander’s passion, and our passion would get it done.”

Zander, who urged his young players to stay on and finish up last season at NEC even if they were frustrated, says he didn’t do any recruiting for the new orchestra.

“It’s not an attempt to reconstruct the past,” Zander said. “We were about setting up a new organization and seeing if people wanted to come.”

Thomas Cooper, 18, a violist who had been in Zander’s NEC orchestra, not only wanted to come, he urged his friends to take the leap. In all, between 25 to 30 players jumped from NEC’s top youth orchestra to the Boston Philharmonic’s.

“All three orchestras in Boston are great youth orchestras,” Cooper says now. “But there’s something special we saw in working with Zander, and we knew we wanted to come.”