For five weeks, the classes they had looked forward to each Saturday were canceled.

Gilberto Pagan, 14, and his sister Eyleen Bermudez, 11, borrowed books about martial arts from the library. Matthew Mascellino, 11, and his brother Masen, 7, sparred in their Summer Hill living room.

Their beloved program, Martial Artists Against Street Violence, had for months provided free martial arts classes to children on the North Side. But the program was in limbo for most of February, when weekly classes were suspended following revelations of the founding instructor's criminal record.

Then, in March, Chun Sik Kim extended a lifeline. The Pittsburgh mogul of an empire of "tang soo do" studios, Mr. Kim agreed to partner with the program's organizer, Seth Cullens, a Central North Side father whose 5-year-old son, Jayden, is the program's youngest student. Mr. Kim handpicked a new teacher.

Since March, when classes began again, the program has reinvented itself. In addition to the new teacher, Dustin Allensworth, of Monroeville, the project has a new name: the Child Safety Program with C.S. Kim Karate. Classes are now held twice each week, Tuesdays and Fridays. And while sparring was a prominent part of the program before its hiatus, the students no longer spar, for now; Mr. Allensworth focuses on simpler technical elements, and above all, discipline.

"I don't think kids like to admit it, but they like the strictness," said Marcy Auer, of Spring Garden, whose son Jonathan Ruby, 8, has attended the classes since they began last year.

Parents said the practice is more focused now, and is devoted primarily to the "art" of tang soo do, a Korean form, instead of kicks and punches.

George Godfrey, of Hazelwood, said that Malachi Farrow, his 8-year-old grandson, has improved his grades since he joined the program.

"I think the kids are doing a lot better," said Mr. Cullens. "We've gotten kids on honor rolls that have never been there."

Marisol Medina, Gilberto and Eyleen's mother, said her children are kinder to each other.

"They've changed a lot, my kids," she said. "Them two coming here, they interact more at home. They respect each other."

And two students who recently vandalized a neighbor's garage but would not own up to their mistake came clean when Mr. Cullens spoke to them after class, he said. They painted over the garage door that night.

"The kids are listening to us more," Mr. Cullens said. "It's a lot more open. These new classes, I think they are a large part of these kids starting to be more receptive."

The students' parents are raising money to take the children to a tang soo do tournament in Orlando, Fla., followed by a trip to Disney World. Mr. Cullens said they raised about $230 at a book sale Saturday despite bad weather and a power failure.

They worked out of the basement of Observatory Hill's Riverview United Presbyterian Church, where the classes are held, and the parents plan to hold another book sale in the same location May 29.

If they raise enough money, the trip to the tournament in August will mark the anniversary of the program, which has survived a rocky year.

Mr. Cullens and the instructor he partnered with, Al Joseph "Yusef" Owens, started offering free classes in August 2009, soon attracting more than 20 regular students. The program was sponsored by a portion of a $10,000 grant from the city, administered by the Northside Leadership Conference. But the Post-Gazette learned in January that Mr. Owens, of Penn Hills, had spent 18 months in jail after pleading guilty in 2006 to drug charges.

Neither the city nor the Northside Leadership Conference had performed a background check on Mr. Owens or required him to obtain the state clearances necessary to work with children. Mr. Owens was removed from his volunteer position Jan. 25.

"I have nothing but great respect for what Yusef was able to do in the program," said Mark Fatla, executive director of the Northside Leadership Conference. "It was unfortunate, but it was also unavoidable."

Mr. Cullens sought advice from Mr. Kim, well known in the city's martial arts community. Mr. Kim, who has spent more than 30 years building his federation, decided it was time to give back.

"I realized I like to help these children with martial arts," he said. "They need help."

Mr. Kim, of Monroeville, hunted for a new instructor, and about three weeks later, he chose Mr. Allensworth.

Tang soo do training typically starts with two weeks of private classes, said Mr. Allensworth. Instead, he tries to mete out the attention of a private class during the program's often hectic sessions.

During a practice Tuesday, Mr. Allensworth negotiated a balance between discipline and patience, rousing choruses of "Yes, sir!" from the class of 21 students. He handled a cascade of bathroom requests with humor and grace, allowing a small exodus to prevent an avalanche.

And when Mr. Kim arrived, inspiring a terrified awe in the students -- whose eyes grew wide -- Mr. Allensworth flitted around the room fixing uniforms and reminding children to speak up.

As Mr. Kim lectured the students, Masen sat still with a rod-straight back. When Mr. Kim asked the room what "discipline" meant, Masen stood.

"It means that when somebody tells you what to do, you do it," he said, then glanced at his father.

Michael Mascellino returned his gaze and smiled.

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