The number of referrals to child and adolescent mental health services in England has increased by 26% over the past five years, Education Policy Institute (EPI) research suggests.
Its report also reveals one in four referrals was either rejected or deemed inappropriate for treatment.
Out of 60 providers questioned, 54 gave a response.
The Department of Health said it was investing an additional £1.4bn into mental health services for children.
The figures, shared with BBC Radio 5 live Investigates, were compiled using Freedom of Information (FOI) requests submitted to child and adolescent mental health services (Camhs) and local authorities in England.
Some providers in England were unable to give the full information requested - 33 supplied data about numbers of referrals over five years.
Based on these figures, mental health referrals for under 18s increased from 157,000 in 2013-14 to 198,280 in 2017-18.
According to data from more providers - 50 in total - for 2017-18 alone, children and adolescent mental health referrals topped 264,000.
According to the EPI report, around 55,800 children under-18 did not meet the criteria for specialist treatment after being referred in 2017-18.
Some reasons for excluding them from treatment include:
- self-harm referrals accepted only if accompanied by another mental health condition
- a weight loss of less than 15% from their ideal weight for an eating disorder (although this is against National Institute for Health and Care Excellence guidelines)
- young people must have already engaged with early intervention services and waited a specified length of time.
