JOHANNESBURG (AP) -- Dintle Zulu wanted something better for her only child than the worn classrooms, demoralized teachers and defiant students she had faced herself.

So Zulu enrolled Samantha at an elite private school in a wealthy Johannesburg neighborhood, where she, then a cook, and her husband, a furniture salesman, struggled to pay the tuition. Five years ago, under pressure to pay up or withdraw Samantha, Zulu dropped into a modest school near the cafeteria where she worked.

The teacher told her to bring Samantha, now 13, to start the next day, and to worry about paying when she could. She now pays 380 rand (about $50) a month, while private schools for the rich can easily run to move than $1,000 a month.

As the public school system collapses in South Africa, a free market replacement is emerging: Private schools for the poor. Such schools are also coming up elsewhere in Africa and in the developing world. In South Africa, they cater to poor Africans left behind in a system that has struggled to close the gap apartheid created between white and black schools.

The picture is not all rosy: Some schools stay in business just long enough to collect parents' money, and there are questions about who ensures the schools are safe and deliver what they promise. The schools also lack the manicured playing fields and high-tech classrooms of private schools for the rich. But the pressure to stay in business means that they deliver the good grades and strong discipline parents demand.

Only a third of third-graders in South Africa meet the minimum literacy and numeracy standards, according to national test results. Last year, a third of those taking final-year exams failed.

"We must acknowledge that there is poor teaching in many of our schools," education minister Angie Motshekga told reporters when last year's dismal exam results were announced. "Management in our schools is often weak and lacks leadership and commitment. Our systems are also often inefficient."

Researcher Ann Bernstein said she had long wondered why South African parents weren't taking to the streets to protest the poor education their children were getting. So a team of researchers from her independent Centre for Development and Enterprise set out to investigate no-frills private schools.

"Some parents are just voting with their feet," Bernstein said. Parents are "not apathetic. They're not sitting and waiting for the day the education system improves."

Over two years, her team found more than 100 private schools in poor neighborhoods of Johannesburg and rural areas in eastern South Africa. Most of them had been operating for more than a decade, surprising experts who had expected far fewer schools and assumed most went out of business in a few years.

A quarter of the schools Bernstein studied had not registered with the government, making them illegal. Parents who send their children to illegal schools have no guarantee state standards are being met or diplomas will be recognized.

Children are taught in abandoned factories and office buildings. The schools have aspirational names like Freedom and Phoenix.

In many cases, parents encourage teachers who impress them to open schools. Samantha's Progressive Primary dates to 1991, when a Christian school in downtown Johannesburg went out of business and parents persuaded several of its teachers to start their own school.

On average, the schools charged about 700 rand ($100) a month, much less than wealthy private schools, but more than the 100 rand ($15) a month for public schools in the same neighborhoods. After comparing assessment test results, Bernstein's researchers wrote in a report that "private schools are no worse than public schools, and significantly better in some areas."

At poor private schools, administrators at times have to be patient about getting paid, but parents are demanding. If kids' grades drop or a discipline problem crops up, the parents change schools, Bernstein said. As a result, the entrepreneurs who run such schools keep classes small and show little patience with teachers who don't perform, even if, to keep costs down, many of the teachers don't have the qualifications to work in public schools.

Qualified or not, teachers are dedicated, Bernstein said.

At Progressive, head teacher Sonja Kruger said that as a white South African, she was given the best that the state had to offer under apartheid. Now, she said, she has a responsibility to give back. She earns 7,000 rand (about $1,000) a month after 15 years at Progressive, about half the average salary for a teacher in Johannesburg. Kruger started as the school's secretary and has taught for the last six years. Most of the other teachers and all the students are black.

"When you see the kids achieving, it's payback," Kruger said. "I'd say every single teacher that's here is passionate. They have to be, because they're not in it for the money."

Progressive Primary is in what used to be the headquarters of a chain of coffee shops, squeezed between a copy shop and a parking garage. Kruger has noticed similar schools opening in the neighborhood, and says the competition is good for poor kids.

"I don't see why, because they don't have money, their education shouldn't be as good as anyone else's," she said.

Progressive's motto: "Let us shape your child into a top achiever." It has sent graduates _ with scholarships _ on to some of Johannesburg's most demanding high schools.

When he speaks of his years at Progressive, Victor Tshilombo, 24, now a second-year medical student at Johannesburg's premier University of Witwatersrand, keeps returning, a note of astonishment in his voice, to the fact that he spoke no English when he arrived. He had been passed from year to year at his previous public school. Progressive teachers put him back five grades, and embarked on intensive lessons.

Tshilombo said he developed determination and confidence. That was important after he graduated from an elite Johannesburg public high school, when he had to work for two years as an army ambulance dispatcher because he did not have the money to go to medical school. Finally, Witwatersrand offered him a scholarship.

When he becomes a doctor and starts a family, he'll be able to afford more expensive schools, but he does not believe he'll find better than Progressive. He remembers the attention he got when he struggled, even though "my father wasn't rich. I don't think he even paid school fees on time."

At Progressive, 13-year-old Samantha praises her teacher for being "always present. He has never been late to school."

It may seem minor, but teacher absenteeism is a crisis in many public schools. Zulu does not blame the teachers entirely: Their salaries are low, and morale even lower. Most black teachers received the inferior education reserved for blacks under apartheid, and now struggle to meet the new government's higher standards. They also battle in ill-equipped classrooms with students who seem ready to protest at the slightest provocation.

In the 1970s and 1980s in public schools, young protesters were celebrated for risking their lives to stand up to apartheid. Some of today's students seem to feel protest is their birthright.

"In Soweto, you know, we really are disrespectful to the teachers," Zulu said. "I still see kids roaming around the streets during school hours."

Bernstein said discipline is a key demand of parents at the schools she studied. Progressive's head teacher, Kruger, said the school respects the law against corporal punishment, but many parents ask that their children be hit if they misbehave.

Critics worry that such schools will only widen the gap between the haves and have-nots, as the most committed parents and the most promising students leave already troubled public schools for private ones. They also worry that governments will turn over the bulk of the responsibility of education to private schools, wealthy or poor.

"If the public system does not work for the poor, it is a failed state, then you're letting the market take over something that's basic and fundamental," said Wongani Grace Nkhoma of the Open Society Initiative for Southern Africa. "States have to understand that they have the responsibility to provide education that's of good quality, to every child."

For next year, Samantha has been accepted at a competitive public high school with an emphasis on science and technology.

"I'm so ready for high school and all its challenges," Samantha said. "I do realize how lucky I am."