Nonetheless, many of the first students Martins took under his wing are already working as musicians and music teachers.

And the Paraisopolis students who gather every Thursday are enthusiastic about their future. Yanca has a modest dream to become a music teacher for other slum children like herself.

"I play with all my heart," she says, breaking down in tears. "If it weren't for music, I'd be a drug addict or a prostitute or out robbing. Because that's the reality here."

More from CNN Heroes: