The restructuring comes amid a possible $400 million budget deficit, but officials say they will find the money.
"We think we have an absolute moral obligation to turn around these schools," David Weiner, an associate superintendent, said at a news conference Tuesday. "Budget notwithstanding, we're going to be moving forward in that direction."
Perhaps the biggest surprise is South Philadelphia High, which was rocked by racially motivated attacks on Asian students last year.
Though its academics remain dismal, the school has made strides under a new principal, Otis Hackney, who is expected to remain.
The 18 were chosen for their historically poor academic performance, plus other reasons - school violence, dropout rate, and neighborhood factors including unemployment and literacy rates.
The schools are located throughout Philadelphia, and cover all grades, though 10 of the 18 are neighborhood high schools, long a trouble spot.
The so-called Renaissance Schools will take one of four forms. Seven will be district-run Promise Academies, most likely with a new principal and no more than 50 percent of current teachers. Three will be Promise Innovation schools, where the principal stays with the right to keep as little or as much of the staff as he or she wants.
Six schools will be Renaissance match schools, given to charter organizations that apply to run them and hire all staff.
Two of the charters will be Promise Neighborhood Partnership schools, run by Kenny Gamble's Universal Companies, but with district input.
Gamble's group received a $500,000 planning grant from the U.S. Department of Education to develop a Promise Neighborhood in Point Breeze and Grays Ferry with intensive social services for children from cradle to college. The model is based on the successful Harlem Children's Zone.
Superintendent Arlene Ackerman praised Universal, saying it had been through the same scrutiny as six other charter operators deemed qualified to run Renaissance schools.
"We wouldn't have done it if we didn't think they were an organization that could get things done," Ackerman said at an unveiling at Vaux High School, a current Promise Academy.
Ackerman hailed the Renaissance schools as a "signature effort" of Imagine 2014, her strategic plan. The first group of 13 opened in September.
Results for the six district-run Promise Academies are encouraging, but preliminary, officials said.
Shawn Williams, a Vaux junior standing tall in the sharp blue blazer and khakis of his school, said that Vaux's being a Promise Academy has meant a world of difference.
Last year, he said, the school was out of control - few rules, little learning, students acting up all the time, just because they could.
Now, Williams said, "it's just better for us to learn here."
"If we do this," the superintendent said, "we can turn this school system around in a matter of just a few years."
But some were not so sure.
"I'm really concerned that we don't have any hard evidence yet to show this model is working," teachers union president Jerry T. Jordan said in an interview. "This is a fad across the nation, and it's unproven."
Some of the 13 current Renaissance schools have seen turnover in teachers and leaders. Some have struggled to find their way, Jordan said.
The move will mean uncertainty for many teachers. Last year, the district guaranteed that everyone displaced by the Renaissance process would have a job at some district school.
But this year, "I'm not going to guarantee that they will all be placed in a district school," said Penny Nixon, an associate superintendent.
Because of the budget uncertainty, it's not clear how many teachers the district will be able to hire, Ackerman said, adding that no one would be hired until displaced teachers were assigned.
At South Philadelphia High, which will keep Hackney but not necessarily all teachers, there was shock and disappointment Tuesday.
"The timing - we've been making some great progress this year," said Dean Coder, math teacher and union representative. "Some programs have been instituted, it's a quieter year discipline-wise, the morale of students and staff seems to be greatly improving. . . . It's like all of our efforts have been for naught."
Helen Gym, a board member at Asian Americans United, which has pushed for improvements at the school, said the designation was "extremely alarming."
"Why the district would refuse to take action last year when the school was in crisis, and now that we've started to stabilize the school, they throw it into upheaval again," Gym said.
Hackney, who learned of the change Tuesday morning, said he was trying to figure out what it would mean for the school - and how to keep the staff focused despite the upheaval.
It was too early to know how many workers might stay or go, he said Tuesday night.
Everyone knew the designation was a possibility, given South Philadelphia's lackluster academics, Hackney said.
"We're a school that hasn't been successful over a long period of time, and the district saw fit to make changes," Hackney said. "If you think about it from the student perspective, how many more classes do we have to allow to go through without making major changes?"
Contact staff writer Kristen Graham at 215-854-5146 or email@example.com.