Community leaders blame a "tremendous hopelessness"
Children should be targeted in the first year of primary school to prevent them from turning to knife crime later, the shadow home secretary has said.
Dominic Grieve said there are primary head teachers "who can point out...children who are going to be a serious problem".
Mr Grieve's comments come as the PM prepares to announce new measures to tackle knife violence.
Last week five people died after separate knife attacks in one day.
Presumption of imprisonment
Mr Grieve told BBC News: "Truthfully, one has to face up to the fact that in the first year of primary school there are head teachers who can point out the children who are going to be a serious problem six or eight years down the road.
"We are failing completely to do anything about it. That's why we should be looking in the long-term to solve some of these problems."
The approach was one of three key ways he said the Conservatives would employ to tackle knife violence.
Dominic Grieve says people carrying knives should face tougher penalties
He also said in the short-term it was crucial to cut down on red-tape to allow beat officers more time on the street, and that there should be tough legal action over knives.
He said: "We are going to have to have tough sentencing.
"In our view there should be a presumption of imprisonment if you are found with a knife over three inches and you can't show lawful authority or reasonable excuse.
"And those using knives should expect long sentences. Wounding people with a knife, even if only a slight wound, is absolutely unacceptable."
On Thursday four men were stabbed to death in London and a fifth died after a stabbing in West Bromwich.
'Shocking and tragic'
A man stabbed in north-west London on Friday remains critically ill.
Prime Minister Gordon Brown said the recent un-related knife deaths were "shocking and tragic," and promised the publication of a cross-government youth-crime plan.
He said the plan, which the government had been working on over recent months, would include new enforcement measures and improvements to sentencing.
A "new approach to youth crime prevention" would involve "tough parenting programmes targeted on areas with the most problems," he said.
Young people are angry. They are confused. They feel a tremendous sense of hopelessness
Reverend Les Isaac
The Ascension Trust
"We will continue to make absolutely clear that carrying a knife is unacceptable in our society," he added.
Earlier, a church conference on gun and knife crime in London said a "tremendous hopelessness" was the root cause of the violence.
At the Bite the Bullet conference in Brixton, south London, youth workers warned the problem would only be fixed by tackling its root causes.
The Reverend Les Isaac, of the Ascension Trust, said: "Young people are angry. They are confused. They feel a tremendous sense of hopelessness.
"If we could go out and say to young people, 'you are worth something, we love you, we want to help', young people will look at their lifestyle and begin to rethink what they are doing."
Mr Isaac, who is a former north-London gang leader, warned knife culture could take as long as 15 years to reverse.
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