Only three health boards met an 18-week waiting-time target for children and young people to receive treatment from mental health services.
Figures from January to March this year show that only 71.2 per cent of young people were seen within the 18-week waiting time.
Data showed 3,979 children and young people started treatment at specialist child and adolescent mental health services (CAMHS) in the same period.
Eleven of Scotland’s 14 health boards failed to meet the target, with only NHS Ayrshire & Arran, NHS Shetland and NHS Western Isles having at least 90 per cent of patients seen within the time.
The Scottish Children’s Services Coalition called for dramatically-increased investment in mental health services that are “fit for purpose”.
A spokeswoman said: “It is clearly disappointing to note these newly-released figures highlighting that the NHS in Scotland, including 11 of our health boards, are failing to meet what is already a lengthy waiting time.
“This is no coincidence given that a very small proportion of the overall NHS and mental health budget is being spent on addressing the needs of children and young people, and yet we know that three children in every classroom has a clinically diagnosable mental health problem.”
The figures also showed that 35 children and young people had been waiting for more than a year prior to being seen.
Mental health minister Maureen Watt said: “Under this government, CAMHS staffing has increased by 69 per cent , with 28 more staff in the last year alone. To build on this, we’re working with boards to increase the recruitment of more specialists.
“While the average wait for treatment is ten weeks, many boards must improve their performance and I will continue to meet with those boards which fall short of our expectations.
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“Our mental health strategy is investing £150 million into services over five years to help reshape how services are delivered for the benefit of patients. “
Alex Cole-Hamilton, Scottish Liberal Democrat health spokesman, said: “Mental health waits for young people are still the poorest on record.
“This critical target is being missed by a huge margin.
“It is appalling to learn that 158 children waited, or are still on the waiting list, for more than a year.”
Anas Sarwar, Scottish Labour’s health spokesman, said: “If these figures were replicated in our A&E wards, there would be a national outcry.
“We hear plenty from ministers about parity of esteem for mental health services and acute services - but these figures show that just is not happening.
“Labour has pressed the government on these failures time and again but the response simply has not been good enough.
“NHS patients and staff deserve better than these continued failures.”
Annie Wells, Scottish Conservative mental health spokesman, said: “It is completely unacceptable that so many children and parents are waiting such a long time to access essential mental health services.
“The fact that more children are waiting longer is inexcusable.
“The SNP has publicly committed to taking mental health seriously but their empty rhetoric is just that; the services are getting worse.
“The SNP has a duty to urgently improve access to services and ensure that all children get speedy and appropriate diagnosis. Anything less is failing children and families.”
Alison Johnstone, health spokeswoman for the Scottish Greens, said: “The fact that so many young people in Scotland have to struggle through mental health problems with little support or care shows we’re letting them down.
“What’s worse is that those who have already taken the brave step by being diagnosed are not receiving the support they need on the NHS.
“How can we improve education outcomes when significant barriers to essential health services for our young people exist?”