If you visit Peter McFarlane's school in Harlem, you may or may not meet him. And if you do, you may or may not realise he's the principal. He could be posing as his own PA; he could be sweeping the canteen floor; and if he's actually in his office, the chances are he's talking to a pupil.
"Every six weeks we test them and every six weeks I talk to each kid," he says. "Why not? What else should I be doing that could be more important? It only takes 10 minutes."
McFarlane - known as Dr Mac because of his doctorate in school transformation - has turned around a failing school, black, impoverished and plagued by drugs and weapons.
When he arrived at Hugo Newman college preparatory school, not a single child was reaching grade level in English or maths. It was failing, in American terms designated a School Under Registration Review. Last year, the seventh year of improved grades, 65 per cent made it in English and 90 per cent in maths. And those statistics have not been contrived - Dr Mac never excludes pupils.
Dr Mac has become something of a role model for neighbourhood schools in the States, not just because of those grade figures but because of his big personality, which enthuses conference audiences with a can-do mentality.
He has been touring Britain at the invitation of the Centre for Public Innovation - a not-for-profit organisation whose goal is to get better results in public services, especially in health, drugs and crime. A kind of Harlem globetrotter, he's been visiting London, Glasgow, Portsmouth and Birmingham. And he's writing a weblog so his pupils back home can keep track of him. Tellingly, they reply to his entries with their own, usually ending in "We miss you".
"We ran a course in the US last autumn on improving children's outcomes, which is where he first appeared on our radar," says Patricia Sauer, of the CPI. "He really impressed the UK delegates, so we wanted to bring him here."
Dr Mac, 43, is a forceful character with an energy and focus that makes what he has done seem simple - the almost inevitable result of putting your mind to a job. "There are different reasons why people take on challenging schools. Some know they can hide there - no great expectations, no great parental demands. For others it's a run to glory - make some changes and then get out. Me, I've been at my school for eight years and I plan to be there a little while longer."
Ask Dr Mac how he does something and you get a nonchalant reply, as if he's asking you what's so difficult about it anyway. Push him a little harder and you find a huge amount of commitment and persistence, sweating away on behalf of his neighbourhood kids in a school once named worst in the city by the New York Times. He's a fine example of Mahatma Gandhi's "You must be the change you want to see in the world".
Still, no matter how many children's names you learn and how much time you spend chatting to them or clearing your brain by sweeping the canteen floor, there is still admin to be done. "How? Well, I work Saturdays too.
The reality is that if you want change you can't make excuses about your personal time. You have to invest in the environment you're trying to change. It's all about middle-class values. I want the things for my neighbourhood kids that you want for your kids, but in Harlem that's going to take a little more time, a little more effort."
Dr Mac - married, black and with a modest amount of bling on one wrist - has heard of but isn't familiar with the detail of Every Child Matters, roughly the equivalent of the US No Child Left Behind programme. There's actually a lot of overlap between the UK strategy and what Dr Mac has done in his school by recognising there is far more to children's achievement than what goes on in the classroom.
"Sure, the first thing you do in a downtrodden area is to improve the environment. You paint shabby buildings and you replace dilapidated buildings. This is what people see first, and the kids feel more valued in a good environment," says Dr Mac, who has published several academic papers on leading schools out of failure. "But other things are going on too. In the States, kids can't come to school without their immunisations. Our attendance was going down from around 98 per cent to 76 per cent because these are kids who can't get to the health centres for their shots and so they were excluded.
"How we approached it was that if you could provide these services on site, they wouldn't lose a day at school. You know, no matter how good the teachers are, if the kids can't come, they're not getting taught."
Dr Mac wanted more than drop-in services. He wanted a full children's health centre, so he found a potential sponsor, whom he rang every day for a year until the poor man agreed to stump up $3 million. "We've got everything now," he says. "Teeth, shots, eyes, social work, psychologist - all on site. We banned unhealthy snack and drink machines too and we set up a school food co-operative to make sure the kids were getting enough fruit and vegetables. And I say all that has a lot to do with my kids'
But other, less welcome, deliveries were also getting through to Dr Mac's 474 pupils: drugs and weapons. Asked how he dealt with that, he answers in his usual deceptively simple style: "Confrontation."
More detail, please.
"This is my neighbourhood. I was lucky when I grew up - good home, good parents. But these kids not being served, being given drugs - it could have been me. I want to prove that kids living in Harlem can rise above the stigma. Now, I know who's selling the drugs and the weapons. I know these guys and these guys have kids. And their kids are where? In my school. So I find the guys and say 'Would you like me to call the police in here?'
Dangerous? Well, if you don't clean your school up, that's a very dangerous place."
You can put up smart buildings and you can put in the health services, but in most downtrodden schools you find downtrodden staff. One imagines Dr Mac sacked the lot and brought in some high-energy younger versions of himself.
"Everyone asks me that. No, I kept all the teachers. What we did was create a sense of urgency around increasing achievement and that meant working collaboratively with the community: the kids, the parents, the staff. You find out what professional development the teachers need and you establish a common language. That's important because struggling schools are fragmented and in need of a common language and a common expectation.
"So instead of firing people I employed a one-on-one tactic. I still meet every teacher three times a year to discuss expectations, professional development and student goals.
"My expectation is my belief. I believe that every child can learn. I believe that if we all work together children can achieve high levels.
"And I use the research. Why re-invent the wheel? Distribute leadership so you can be almost invisible and still the common language and expectation are there. Be smart enough to give others the ideas and make them feel smart. Give them the authority to make change. Plant ideas so that they become other people's ideas, and then when they go run their own school, they take those ideas with them."
Candidates for teaching jobs at Dr Mac's school often find themselves greeted and seated by his conversational PA. They relax and chat while the PA listens. That way, Dr Mac (yes, pretending to be his own PA) finds out rather more about them than he would in a formal interview.
There's nothing orthodox about Dr Mac, who once let one of the pupils show a potential sponsor for a million dollars worth of playground round the school, just saying: "I'm kind of busy today, but let me know by the end of the day if you want to sponsor us."
And did he?
"Course he did. Course he did."