Dr. Walter J. Turnbull says that they look like angels. But the truth is they sound like angels and look like young American kids who could just as easily be playing a game of catch in the street — or be hanging out in a crack house.

Therein lies the amazing grace that makes the Boys Choir of Harlem one of the most provocative singing groups to be born and bred in America. It’s all the glory of the European choral tradition used for the highest of contemporary goals: to believe in the worth of all God’s children and give them a chance to sing their way into a life of respect, integrity and hope.

Currently on tour, the Boys Choir of Harlem performed to a full and appreciative house Saturday at the Maine Center for the Arts. The program began with a half-hour of liturgical music, which was the springboard for the group when Turnbull, music director and acclaimed vocalist, formed the Boys Choir in the 1960s. Certainly, there are boys choirs that are more accomplished and formidable than this one. But few could come close to having both the talent and the emotional impact of this group. To know that Turnbull has worked miracles with these boys, has taken them off the streets of New York and redirected their energies toward Mozart’s Vespers, is something that is acutely present in every note. To hear 12-year-old Daniel Lane sing the high notes of Mozart is to understand more deeply than ever before that faith, hope and love are transformational.

Although church music is the foundation of this choir, it is not the only type of music the boys excel in. Spirituals, a medley of tunes by George Gershwin, works by jazz greats and contemporary hip-hop music made up the rest of the program. In the lighter numbers, the boys danced or struck stage poses that were funny, entertaining and extremely well-executed. They even got the Maine Center crowd on its feet and moving.

In a chilling segment of the show devoted to African music and songs of pride and hope, the boys sang their signature version of “Amazing Grace,” with the soulful Terrence Wright (a Boys Choir alumnus) and the sublimely plaintive Krystan Dany as soloists. The performance brought the house down and inspired an elongated standing ovation and cheers in the middle of the show.

From the stage, Turnbull said hello to Maine residents Steven Pane and Yuri Funahashi, both of whom formerly worked at the Boys Choir organization in New York City. At intermission, Pane, who was associate director with the choir for eight years, spoke of working with Turnbull.

“He’s a hero,” said Pane, who became choral director at the University of Maine at Farmington three years ago. “He has really dedicated his life to saving these children.”

Both artistically and technically, the Boys Choir showed rare style and professionalism. Turnbull has shaped disciplined boys who stay completely on task but are nevertheless uninhibited and fluid whether they’re singing “Laudate Dominum” or shouting “Black boys are born of heroes.”

The organization began as a church choir and has grown in 26 years to an institution of music education for boys and girls, and, more recently, into the Choir Academy of Harlem, a fourth- through 12th-grade school that sends 98 percent of its graduates to college.

“Not only have they learned the beauty of music, but their lives have been saved,” said Turnbull, an exultant and momentous man who could rightly be called a modern-day saint.

Because he expects the most, he gets the best. After seeing and hearing Saturday’s performance, there’s no doubting that angels are, indeed, involved in some very vital way with Turnbull’s work.