Just over 100 children who began receiving specialist mental health care in the last three months of 2016 had waited more than a year to get help.
Figures for the period October to December showed that of the 4,222 patients who started treatment from Child and Adolescent Mental Health Services (CAMHS), there were 101 who waited 53 weeks or longer.
The total compares to 16 patients who had to wait more than a year in the same period in 2015.
Children's campaigners have now voiced concerns that long waits for help could increase the number of families facing a mental health " crisis situation".
Despite the rise in the number of children and young people waiting more than a year, the latest health service figures showed an increase in CAMHS patients seen within the 18-week target time.
In the last three months of 2016, 82.5% of those starting treatment waited 18 weeks or less, compared to 79% in the previous three months and 76.2% of patients in the period October to December 2015.
The NHS in Scotland provides specialist mental health care for children and young people suffering from conditions including attention deficit hyperactivity disorder (ADHD), anxiety, behaviour problems, depression and early onset psychosis.
There were seven health boards that met the 18-week standard but five did not while two health boards saw less than half of all patients in the target time, with 48.3% of patients waiting 18 weeks or less in NHS Lothian and 45% in NHS Grampian.
A spokesman for the Scottish Children's Services Coalition (SCSC) said: " These statistics, while an improvement on the previous quarter, highlight that five of our health boards are failing to meet maximum waiting times, a clear 'postcode lottery' when it comes to treatment.
"In addition, more than 100 of those with mental health issues are waiting more than a year to be seen and we are deeply concerned about what is happening to the more than a fifth of children and young people not accepted for treatment."
The spokesman continued: " As a coalition we are delighted that the Scottish Government has committed an additional £150 million in mental health services over the next five years and that this is to be partly used to bring down child and adolescent mental health waiting times, but we clearly need to do more.
"Families usually experience months of waiting even before a referral to CAMHS.
"The consequent delay in diagnosis and appropriate support can lead to a crisis situation for the child or young person concerned, as well as for their family, and the need for costly extra resources to address this."
Separate statistics showed a 49.1% rise in the number of people working in CAMHS since 2006, increasing from the equivalent of 653.7 full-time staff to a whole time equivalent of 974.7 at the end of 2016.
Mental health minister Maureen Watt (pictured) said the " continued reduction in waiting times is encouraging because it demonstrates that access to services is improving".
She added: " I'm clear that we must continue to reduce waiting times and I will not be satisfied until our 90% target is met.
"In the coming weeks I will be publishing our new strategy for mental health. This will lay out how we will change services over the next decade, backed with £150 million of funding."
Labour inequalities spokeswoman Monica Lennon said: " The treatment of our young people seeking help for mental health issues is a national disgrace.
"No child should be waiting this long for help; under the SNP it's one in five.
"Over 3,000 young people waited more than eighteen weeks for treatment in 2016 and the SNP is refusing to consider our proposals for school-based counselling, which leading children's charities have called for."
Labour has called for every high school in Scotland to have access to a counsellor, with Ms Lennon stating this would " cost a fraction of what the SNP propose to spend on mental health" but could also "make a real difference in terms of support".
Liberal Democrat health spokesman Alex Cole-Hamilton said: " It is a sign of this Scottish Government's lack of ambition that they are celebrating figures showing most health boards still routinely missing waiting-time targets.
"In NHS Lothian, my own health board area, 467 children and adults have been forced to wait over a year for treatment - figures that I certainly don't find 'encouraging'.
"SNP ministers should be embarrassed that they have failed patients to this extent. Staff are working around the clock but they aren't getting the support they need."
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