A qualified counsellor would be employed in every secondary school in England under proposals from Labour.
Labour has pledged to recruit 3,500 on-site secondary-school counsellors and would ensure every primary school had a counsellor visit at least once a week.
According to the House of Commons, an estimated 70% of secondary schools and 52% of primary schools in England offer counselling services.
Concerns over children's mental health have become more widespread.
NHS figures suggest, in 2017, one in eight five- to 19-year-olds had been diagnosed with at least one mental health disorder.
Current Department for Education guidance says schools are central to building pupils' resilience as part of a consistent whole-school approach to mental health and wellbeing.
But it adds: "School staff cannot act as mental health experts."
Announcing plans for "real change", Labour said it would spend £845m per year on its Healthy Young Minds plan to ensure early prevention and identification of psychological issues, as well as access to mental-health support.
A spokeswoman said the party would set out how it would fund the plan when it published its manifesto.
The party has also vowed to establish a network of drop-in mental-health hubs to enable 300,000 more children to access support directly.
And it has pledged to work to develop and publish a national strategy to address adverse childhood experiences and trauma.
Labour leader Jeremy Corbyn warned failing to help young people would store up problems for the future for a whole generation.
"Almost every day someone talks to me about the terrible stresses a child or young person they know are going through," he said.
He said every young person "deserves the support they need for their talents to flourish and to play a full and positive part in the life of the community".
"Our Healthy Young Minds plan is a vital investment in the lives of our young people and an investment in our country's mental health," Mr Corbyn said.
Shadow health minister Barbara Keeley said the government was failing young people.
"Our young people deserve better and our country needs real change to tackle the emerging major health crisis in children's mental health," she said.
"Labour will ensure every school has a qualified professional on hand to support young people with their mental health, [and] create a network of open-access hubs for children to access mental-health services without waiting months for an appointment."
The Conservatives have said they would introduce mandatory health-education lessons from 2020.
"This will ensure pupils are taught about the benefits of a healthier lifestyle and how to build mental resilience," the party says.
"It'll also cover how to recognise common signs of mental illness and how to cope and react in the modern world."
The Tories also say they would invest £300m over the next three years to deliver the Children and Young People's Mental Health Green Paper "to do even more to help young people get the mental health support they need".
The Liberal Democrats say they would invest £11bn into mental health services such as child and adolescent mental health, matching waiting-time standards to those in physical health and expanding the mental-health workforce.