Plan B returns to his old school sin-bin – but this time as mentor

Musician trains east London youths to perform with him on stage

Plan B, top, Leona Lewis and Labrinth working on Project Hackney (BBC)

The musician and film director Plan B has returned to the pupil referral unit that he attended after being thrown out of school and is training a group of troubled teenagers to perform at the biggest concert to be staged in Britain this year.

Plan B has spent more than six weeks preparing the young group to perform at the Hackney Weekend festival in London later this month, an event which is being broadcast on BBC Radio 1 and will be attended by 50,000 people.

Working alongside the singer Leona Lewis and the producer Labrinth, Plan B, real name Ben Drew, went back to the Tunmarsh Pupil Referral Unit in the London borough of Newham, to which he was sent as a 15-year-old after throwing a chair at a teacher. In his lyrics the singer and rapper has described his difficult upbringing in Forest Gate, east London.

The children who will perform at Hackney Weekend are as young as 13 and were sent to Tunmarsh for a range of misbehaviours that included acts of violence and carrying a ball-bearing gun into school. Some of the children have been the victims of serious bullying or have behavioural problems resulting from attention deficit hyperactivity disorder (ADHD).

The project, filmed by the BBC, encountered significant problems and the artists are shown expressing their doubts. At one stage Plan B, 28, resorted to calling the teenagers into a room and issuing them with an ultimatum. "When I leave here and you are not doing the right thing I am failing and you are failing yourselves," he said. "You are proving all them people out there that think you are stupid right – and they ain't right."

He was returning to the unit for the first time in 12 years and admitted that the teachers had helped put an angry young man on course for a successful music career.

Many of the children selected by Plan B had minimal previous experience of music. Justin, 13, who has ADHD, had never picked up drum sticks before Labrinth taught him how to play. Jesus, 13, was encouraged to rap and to produce beats on a computer after he told Plan B how he had witnessed his friend being stabbed to death in the street.

Plan B and Labrinth were at pains to encourage the teenagers to seek a positive message in their music. Plan B warned them: "You cannot be performing songs about money and hoes (prostitutes) and cars and all that – I'm not that kind of guy. I want you guys to write about your saddest ever moment and how you truly felt about it." Labrinth said: "To them, to be in the slums and in the ghetto is a cool thing. I'm [telling them], 'It's not really, mate'."

Plan B said: "I hope that they feel that sense of achievement and I really want to see if it has made their life better. And [if] they are closer to accepting some of the things in their life that aren't their fault that have been holding them back, I feel that's the biggest accomplishment."

''Project Hackney' will be shown on BBC3 at 9pm on Sunday