Johannesburg - "Big brother Roger," as the village schoolteachers call him, smiles at the small children and asks them to guess which sport he plays.Most of the bright-eyed three-year-olds have no idea who their visitor is but one, quicker than the rest, pipes up: "You play tennis!".Delighted, Roger Federer turns his palms up to reveal a badly calloused right hand punished by 23 years of holding a racquet, showing the children the difference from the smoother left one.There are few parts of the world where the man considered as the greatest ever tennis player and holder of a record 17 Grand Slam titles is not instantly recognised.Here, in rural South Africa where he is visiting one of the village pre-schools his charitable foundation supports, the Swiss is unfamiliar to the children but commands their attention and curiosity.In a small, cool, classroom, the toddlers sheltering from the heat stand with heads tipped upwards and eyes fixed on the towering champion as he hits a tennis ball against a wall, demonstrating how to swing a racquet.Federer looks composed in the sweltering heat of Limpopo province, on the border with Zimbabwe, even though his bright red shirt, wet with sweat by noon, gives him away.Deep in the densely vegetated village some 20km from the nearest paved road, the ground is parched and dust flies into the air as brightly-costumed Venda women dance to entertain their world-famous guest."My heart is in South Africa, through my mum," Federer, the son of a Swiss father and a South African mother, told Reuters."My mum being from here, me spending a lot of time here as well, I feel most connected to this part of the world."The Roger Federer Foundation supports 40 pre-schools in the area and spends over $3m a year on educational projects in South Africa, Botswana, Zambia, Zimbabwe, Malawi, Ethiopia and Federer's home country Switzerland. Over 50 000 children benefited from the foundation's efforts in 2012 to improve quality education in pre-schools and primary schools."When I travelled the world, I definitely saw poor countries, people who told me it was so hard for them to get an education," said Federer, who was visiting two pre-schools in the Limpopo province with his mother this week to mark the 10th anniversary of his foundation being founded."I always liked the idea of education because in our world going to school is the most normal thing in the world. We sometimes forget what a privilege it is, to go to school."South Africa has a broken education system, inherited from decades of inferior education for the majority black population under the apartheid system.Nineteen years into democracy and the new government is still overwhelmed by the task, with some high-school leavers managing pass rates of only 30 percent.In this place, a decent education remains beyond the reach of many children and some 80 percent of the community is unemployed, the village chief's representative said.For a man who has earned close to $80m in prize money alone thanks to his exploits on a tennis court, Federer has never forgotten the value of a good education.Federer admits he did not always do his best at school, saying: "I used to have many more regrets when I was younger, because I was a bit crazy."At school, I wouldn't always learn for my tests as much as I should have. I think that's why today I'm so dedicated to both things, so people don't do the same mistakes as I did, even though I was able to turn the corner in time."The father of twin daughters, Federer added: "I like to be an idol for kids, I do. For me it's important to be a good role model and I live accordingly."But I'm not changing for it, I do it because I believe in it and because it is natural."During his three-hour visit to the pre-school in Guvhu, Federer held a captive audience as he read the story of the 'Gingerbread Man' out to the 30 or so children who sat around him.As his visit comes to an end, Federer leaves with the words of the village school principal echoing in his ears: "If it is possible, please, come back to us again."