When he was 12, he was left on the sidewalk by his mother. Now, he heads the largest Sunday school in the US, reaching more than 20,000 children every week. Nick Morrison meets the preacher who's determined to make a difference.

BILL was walking down the street with his mother, near his home and the hotel where she worked as a barmaid. They sat down on a concrete culvert over a ditch by the side of the road, and after a few minutes his mother stood up.

"She said: 'I can't do this any more. You wait here,' and she walked away and she didn't come back," Bill recalls. "So I sat there for three days."

So it was that at 12, his father dead and his alcoholic mother having abandoned him, Bill was alone. As he tells it in his Florida drawl, he was old enough to know something was wrong, but too young to have the initiative to do anything about it. So he sat and he waited.

"I was there for three days. No food, no water - that was it, you know? Strangely enough, it was not until about that last day that I really started thinking: 'This isn't good. This is not good'."

Eventually, a neighbour stopped, took him home, fed him and sent him to a Christian youth camp for a week. It was his first experience of religion, and it was a defining moment in his life.

Now, Bill Wilson, or Pastor Bill as he is known to thousands of children, is the leader of the largest Sunday school in the United States, and he can trace it all back to that neighbour who stopped at the roadside.

"For the first time in my life I remember feeling like somebody really did care for me. Out of all the people who walked by me and drove by me, it seems like there is always one. The crowd never understands that one person can make a difference.

"It is always the folks that just have the heart. It is not about circumstances, it is not about the situation, it is about the Christian man who had a heart for a young boy who had nobody."

Bill, now 55, is on one of his frequent trips to Britain, promoting the Metro Ministry he founded nearly 25 years ago in New York, and raising funds for his work. Tall and lean in dark slacks and red checked shirt, he cuts a distinctive figure with his thick, shoulder-length hair. His dark eyes have a mesmerising stillness about them, although they seem to move independently.

He never seems to tire of telling his story. Of how he was abandoned and then picked up off the street. How he spent four years living in a six foot square broom cupboard at his local church with a piece of foam rubber for a mattress and surviving on left-overs brought by the congregation each evening.

After graduating high school, he went to work for Ford, but at 19 enrolled in a Bible school. It set him on the road to becoming a pastor, but he says it was not so much a calling as simply doing what he ought to do, a view borne of his own experience: the man who found him didn't have to pray to do the right thing, he saw a boy in need and he stepped in.

'PEOPLE speak a lot about the call of God. That never happened to me. To me, the need is the call. If you see a need, you can feel that and it if it is within your capabilities, that is the call of God," Bill says.

He moved to Maryland to set up a Sunday school, then in 1980 went to Brooklyn, a challenge both to himself and to his faith.

"If the Gospel is supposedly what we have held it is, then I needed to put it to the test. If it doesn't work in the ghetto, then maybe it is not true at all."

He was the only white person in a neighbourhood of blacks and Puerto Ricans, and it was hard. "The first eight years were so painful," he acknowledges. He paid a drug addict to dress up as Yogi Bear, and paid a dealer to drive a bus around the streets, promoting his Sunday school. He rented a building, and the first day more than 1,000 children turned up.

Now, around 20,000 children turn up every week. He describes it as a "Christian Sesame Street", using songs, skits and games to get the message across.

His Metro Ministry has 161 full-time staff and 300 volunteers, but he still lives in the neighbourhood - they are still the only white people - and he still drives the bus to pick up the children. Every one of the 20,000 children receives a visit from a Metro worker or volunteer every week.

"My whole premis is getting out of the box. If you want something you have never had before, you have got to do something you have never done before," he says.

But it has been a difficult journey. He was stabbed in a fight on a bus, he's been threatened with being set on fire and his ribs were broken in a street robbery. He was hit in the face with a brick, breaking a front tooth and leaving him temporarily blind in his right eye. "That's why my eyes move like they do," he says.

Last year, during a robbery, one of his attackers put a gun in Bill's mouth and pulled the trigger. The first time it didn't go off, the second time the bullet went through his cheek. He drove himself to hospital.

He says he's seen 22 murders up close. One of his assistant pastors has been murdered and a volunteer has been raped. His voice starts to crack and those eyes turn red when he tells how only the other week a newborn baby was found in a garbage can. But he's stuck it out, and in the process earned respect from the neighbourhood.

"We're part of the neighbourhood now. They saw the perseverance; it was the perseverance that spoke to them," he says. "People don't really care how much you know, until they know how much you care. Now the drug dealers are sending their little brothers and sisters and their kids to Sunday school, because they don't want them to turn out like they did.

'I'M not nearly as interested in what they become as in what they do not become. They may not become doctors, lawyers, pillars of the community, but they do not become drug addicts and prostitutes. To me, it is about prevention, not intervention.

"I'm not afraid to talk to drug dealers, be around prostitutes, mix it up on the street. I'm not afraid of anybody. I have earned the right to be heard."

He found his mother 20 years ago. She didn't remember having abandoned him. He says he tried to stay in touch, but "she just was not open for it". Four years later, she was found dead on the street with a whisky bottle in her hand.

"It doesn't matter how I feel about, life goes the way it goes. That chapter is closed," he says simply.

Despite everything that's happened to him, Pastor Bill is not going to play the victim. He chose to take a different path.

"In America we have this everybody-has-been-abused syndrome, but you know what? We have all been abused. So what? You want to use that as a reason to be an idiot for the rest of your life? Or do you want to take the things that have happened to you and use it to help somebody else?"