Many end up in unsuitable adult psychiatric wards, children's homes or secure accommodation because of a shortage of places.
According to the Office for National Statistics, around one in 10 youngsters is affected by a mental health disorder. Yet the report published by the children's charity YoungMinds shows tat even when a need for immediate hospital admission is diagnosed, children face a wait of up to three weeks.
In a secondary school of 1,000 pupils, around 50 will be seriously depressed and 100 will be suffering significant distress. But there are just 81 child and adolescent units in England and Wales, accommodating only 972 patients.
The report "Whose Crisis? Meeting the needs of seriously disturbed young people" is at www.youngminds.org.uk