Analysis of Information Services Division Scotland data by Scottish Labour shows that 315 young people waited 53 weeks or more to begin treatment for child and adolescent mental health services in the past year.
The figures were criticised by the party, whose members said longer waiting times for mental health services could worsen the conditions of patients.
The party also said there had been a ten per cent cut in the number of educational psychologists under the SNP.
Monica Lennon, Labour inequalities spokeswoman, called for the Scottish Government to support Scottish Labour’s plan.
She said: “These are shocking figures. No young person seeking treatment should be waiting more than a year, but more than 300 is a national scandal.
“The longer a patient has to wait for treatment the more likely it is that their condition will get worse along the way.
“Labour wants to see more than just warm words from the SNP government’s mental health strategy. A good starting place would be backing Labour’s plan for guaranteed access to a qualified counsellor for every high school in Scotland.”
The Scottish Government, however, said the number of child and adolescent mental health service (CAMHS) psychology posts had more than doubled since 2009 and the overall workforce had increased by 30 per cent.
Minister for Mental Health Maureen Watt said: “Scotland was the first country in the UK to have a mental health waiting times target, a sign of how importantly we view this issue.
“However, treating young people when they are ill is only one part of the mental health story. We must develop new and innovative ways to improve mental health, intervening early to prevent illness and to support people to manage their own conditions and well-being.
“This will be a major priority for the forthcoming Mental Health Strategy which will set out our 10 year vision for transforming mental health in Scotland. The strategy will be backed by an additional £150 million over five years.
“A national review of health and social care targets is already under way led by one of Scotland’s renowned medical experts, Sir Harry Burns.”