All young people in the UK should have access to school counsellors to tackle an "epidemic" in self-harm, the government has been been told.
Baroness Walmsley said the problem was worse among young women and girls.
But instead of hiring more counsellors, who could offer free and non-judgemental support, schools were having to sack them to save money.
The government said it would shortly release "quite ambitious" proposals to improve young people's mental health.
It has already promised £1.4bn for mental health services for children and young people up to 2020.
But critics say too little of that is being spent in schools, where children need it most.
Baroness Walmsley said: "School counsellors can be a very valuable resource in helping to tackle this terrible epidemic of emotional distress amongst young people, because they are non-stigmatising and easily accessible."
She highlighted research that showed a 68% increase in young girls being treated in hospital for self-harm injuries.
The Liberal Democrat peer called for the government to guarantee a counsellor for every state secondary school by 2022.
Health Minister Lord O'Shaughnessy said the government was funding "mental health first aid training" in 1,000 schools, adding "the ambition is to grow that to all secondary schools".
But campaigners say that is no substitute for counsellors, whose sole job is to listen to children's problems in a confidential environment.
Sammy Barry, a 21-year-old part-time youth worker and Lib Dem activist from Hemel Hempstead, in Hertfordshire - an area where counsellors are thought to have been made redundant - said they played a vital role.
"A lot of the time children don't want their parents to know what is going on. Sometimes the parent can be the problem," she told BBC News.
"Children spend most of their time in school so having a counsellor there really helps. It is easily accessible and free - somewhere they can go when they are having a tough time".
She said teachers could find themselves "under a lot of pressure when they are not supported by counsellors".
Lord O'Shaughnessy said he would look into claims counsellors had been made redundant in Hertfordshire schools.