Expelled from school at just 14, Marvin Osemwegie spent his days wandering the streets of Peckham, south London, getting in with the wrong crowd.
Written off by the education system and by his family, it was only a matter of time, he said, before he would have found himself in the wrong place at the wrong time.
"I could have chosen to go one way or another," Mr Osemwegie said.
"I was going left - I was out of school, I had nothing to do, I was hanging around in gangs.
"It was only a matter of time before you're in the wrong place at the wrong time.
"But when I came here [From Boyhood to Manhood], slowly by slowly, I left that kind of lifestyle and became part of something great."
Enrolled in the From Boyhood to Manhood (FBTM) day programme, Mr Osemwegie joined other youngsters excluded from mainstream education and was taught how to turn his energies to something positive.
The organisation was set up in 1993 to help young black boys escape the deadly culture of gangs, drugs and violence.
Mr Osemwegie said: "It had a great effect on my life because it helped me with my self development, with my temper, and I learned how to control myself.
"It meant I was able to go out there and have an effect like I was supposed to, rather than going out there and being a nuisance wherever I went."
After two years in the programme, Mr Osemwegie went to college, where he gained five GCSE's and then three A-Levels.
Now, aged 21, he is studying film and business studies at Kingston University in London and hopes to become a film producer.
It is light years from where he could have ended up.
"The way I am able to judge it is by the people I used to hang around with," he said.
"A lot of them have ended up in prison, shot or drugged up in a madhouse somewhere.
"I'm not saying this is how I would have ended up - I might have ended up working at McDonalds from nine to five. But when you look at these things, it makes you think."
Mr Osemwegie is one of a group of former FBTM students now forming their own business, Streets 2 Success, which will mentor young boys in the area and help them fulfil their ambitions in life.
Uanu Seshmi, director of the foundation, said for many gangs of disaffected youths in the area, carrying weapons was not only common, but had become seen as a necessity.
Since he helped found FBTM in 1993, the organisation's day support centre has taken in 400 students and, in total, about 11,000 young people have been involved in the centre's workshops.
"We take in boys who have been excluded from school," Mr Seshmi said.
"These are boys who nobody wants to be around - who people want to run away from or at the very least cross the street to avoid.
"We have a culture in which using a gun is the way to express yourself as a man - the more violent and tough you are, the more people respect you as a man.
"This is about disrupting this type of mentality, getting them to think outside the box of what a man is and exposing them to a different type of manhood."
Mr Seshmi said behind the tough image of many young gang members they suffer from low self-esteem and a lack of confidence and often lack positive role models in their lives.
He said: "When you go home and see your mum being beaten up, you've seen your friend being stabbed to death, your sister being used as a prostitute - a lot of these guys have been through terrible things and are in pain.
"Their relationships are based on fear, on dominating and exploiting other people, and they are very limited in how they relate to people.
"The best way is to build positive achievements and show empathy over a period of time.
"If you find a young kid in a stressful situation, it would be a foolish thing to try to coerce them. You have to observe yourself and see how you are speaking to that child.
"In that way you are understanding that person and that child feels you care and understand."