Ken Okoth, 30, who teaches at the Potomac School in McLean, left his home in the slums on the outskirts of Nairobi in 1997 for a scholarship to St. Lawrence University in Upstate New York. He went on to get a master’s degree, marry a fellow teacher and settle in Washington. But strong ties to his home remain. Not only does Okoth support his mother and several family members, but for the past several months, he has been the de facto head of the Red Rose school in his old neighborhood that serves orphans and other impoverished children of the slums that ring Nairobi.