Research by the NSPCC found a total of 34,757 referrals for specialist support were made by schools in 2017-18 – the equivalent of 183 every school day.
This is compared to 25,140 referrals in 2014-15.
More than half of the referrals came from primary schools, where children are under the age of 11, the figures showed.
The statistics also revealed that nearly a third of those referred to NHS Child and Adolescent Mental Health Services (CAMHS) were declined specialist treatment.
The NSPCC warned increased demand for services was placing the system under pressure and jeopardising the well-being of thousands of children.
It has called for more funding for its Childline service to help relieve some of the pressure.
Peter Wanless, chief executive of the charity, said: “Our research shows schools are increasingly referring children for specialist mental health treatment, often when the child is at crisis point.
“We have seen a marked increase in counselling about mental health, and fully expect it to continue.”
The NSPCC’s data, released under the freedom of information act, covers 53 of the 66 health trusts known to provide mental health support to children.