In the last five years in the UK, more than 100 children have died from knife wounds. But violence isn't inevitable and evidence shows that we need more mentoring, therapy, family support and police in the areas where violence is high. So why don't we do what works? Jon Yates from the Youth Endowment Fund looks at the schemes that have successfully reduced knife crime. He investigates why the lessons they've taught us haven’t been scaled up. And why we’re spending money on other things like knife awareness campaigns without any evidence they work.