The school on the edge of Kibera houses more than 500 lively children, 70 percent of them orphans, dressed in green uniforms.
More than 30 of the children are HIV positive and receive anti-retrovirals from a nearby clinic in the slum, supplied against vouchers from the school.
The small size of the premises means classes are noisy and overcrowded, with up to 80 children of mixed ages. The school, headed by dynamic Kibera resident Josephine Mumo, has proven skilful in raising support.
Singer Harry Belafonte, Barbara Bush, mother of President George W Bush, and actress Drew Barrymore have been backers.
Without their grandmothers and projects such as Stara, many more orphans in Kibera and elsewhere would end up as glue-sniffing street children or child prostitutes.
Josephine Mumo says that when the mothers started the school, they brought in children who had been raped as they went door-to-door begging for food.
SURVIVE FOR THE CHILDREN
Many of the grandmothers are themselves weakened by HIV as well as old age, making it even harder for them to feed their charges.
Peris Owuor, 50, is a Kibera grandmother looking after seven grandchildren. "Sometimes my body does not feel good and I cannot go to look for food," she said.
Owuor, whose husband died of Aids in 1998, washes clothes to make money, at 150 Kenya shillings ($2.25) a day, and tries to help feed her three surviving children who have no jobs.
"But when my body is not good I just have to stay at home."
Another grandmother, Antonina Mujenge, also HIV positive, cares for five of her own children and four grandchildren. She also sells charcoal.
"I try to look after them like other children but it is very difficult because of my low income. Sometimes there is not enough for all of them," she said.
"My main aim is to stay around long enough to make sure the kids can get an education and find jobs," said Mujenge, who has lived in Kibera for 20 years.
She would love to return to her village in western Kenya. "But I am an outcast at home. They say I can infect others. I cannot go back."
Grace Atema, 65, looks after three grandchildren and her daughter, mother of two of them. She washes clothes twice a week to raise money.
"I put everything I get towards the children. But I worry what would happen if I died. How would they survive?" she said.
