Cecil Mong, aged 15, complained of the lack of positive black role models.
"The American rappers rap about having a lot of money, blowing it on girls and shooting people," he said. "These are the kind of people that black youths look up to, but they are not positive enough to help them think that they can achieve in life."
Dr Roselle Antoine, principal of local tutorial college TCS, received applause and cries of "That's right!" when she said that parents could do more to support their children. But several mothers said that schools were also to blame, with two saying their children had faced discrimination from white teachers.
Gerald Anderson, a record label manager and entrepreneur, said he feared for his future customers. "The boys go to school with a lot of anger for no reason," he said. "And no one deals with it because there is too much political correctness."
The event's organiser, Ezi Onyemaechi, runs Dayspring supplementary school in Stonebridge, which offers Saturday lessons to five to 16-year-olds.
She said the debate showed there were issues to address, and she will pass on a full report to Brent education authority.