'Treatment gap' in youth mental health services
More than a quarter of young people referred to specialist mental health services in England are rejected for treatment, says a think tank study.
The Education Policy Institute (EPI) says 133,000 were turned away last year, including people who had self-harmed or experienced abuse.
The report warns of average waits of almost two months and a system struggling to cope with the demand.
An NHS spokesman rejected the report as a "flawed analysis".
"The NHS is actually ahead of its target on ensuring as many children as possible receive mental health care - seeing an extra 53,000 children, teenagers and young adults last year, a 14% increase on the year before," said the NHS spokesman.
The NHS accused the report of using misleading measurements - arguing that it was wrong to assume that young people not given treatment by NHS mental health services were "left to fend for themselves", rather than being directed to get support elsewhere.
The EPI report, based on Freedom of Information responses from mental health service providers in England, warned of "patchy" provision for children and young people and a system "under great strain".
"There is a vast treatment gap, meaning the needs of hundreds of thousands of young people in England are not being met," said report author Whitney Crenna-Jennings.
The most common reason for the rejection of 26% of referrals to child and adolescent mental health services (CAMHS) was because children's conditions were not suitable for treatment or they "did not meet eligibility criteria".
But the report raises concerns about a lack of consistency and transparency about support available to young people with serious problems.
'Deprived of access'
The average waiting time of 56 days is an improvement on 2015, when it was 67 days. But the report warns of significant regional variations, with waits of more than 180 days in west London.
David Laws, institute chairman and former education minister, said progress has been "hugely disappointing".
"Young people continue to be deprived of access to specialist mental health treatment, despite the government claiming significant investment in mental health services over the past five years," he said.
"This report confirms what schools know only too well - that thresholds for children's mental health services are often too high and waiting lists too long," said Geoff Barton, leader of the ASCL head teachers' union.
Vicki Nash of Mind, the mental health charity, said the report's findings were "deeply concerning".
"We know that particularly for young people, timely and appropriate help can prevent further issues in later life. Too often the NHS is failing to provide this," she said.
The NHS says it is planning to increase spending on mental health services more quickly than the overall NHS budget, which it says will be "worth at least £2.3bn a year by 2023-24".