Schoolgirls in England are increasingly at risk from emotional problems, according to a new study.
Researchers from University College London and the Anna Freud Centre compared questionnaires filled in by 1,600 11-13 year-olds in 2009 with similar surveys conducted in 2014.
The report found that the number of girls at risk from emotional problems rose from 13% to 20% over the five-year period.
A mixed classroom of 30 children is likely to contain three girls with emotional difficulties compared with one or two in a similar class in 2009, the study found.
The number of youngsters experiencing other mental health difficulties did not change significantly, according to the study.
Lead author Dr Elian Fink said: "Five years is a relatively short period of time, so we were surprised to see such a sharp spike in emotional problems among girls.
"The fact that other mental health issues stayed about the same makes us think that there must have been significant changes over the past five years which have specifically affected young girls.
"Whatever is causing the rise of emotional problems, it is clear that we need more effective interventions. These might include encouraging teachers to look out for emotional problems in young girls and increasing provision of youth mental health services."
The study, published in the Journal of Adolescent Health, sampled pupils who were matched by age, gender, ethnicity, eligibility for free school meals and the overall socio-economic mix of their schools.
Researchers noted that the classes sampled were not nationally representative as 38% of the children were from ethnic minority backgrounds, compared with a national average of 20-25%.
The study's co-author Dr Helen Sharpe said: "The data we looked at contained more children from ethnic minority backgrounds than the national average, so the study is not representative of England as a whole.
"However, our data did not show significant differences in emotional problems between children from different ethnic backgrounds. As a result, I think we can be confident that the increase that we saw would apply across the board despite the unrepresentative sample."
The schoolchildren completed online questionnaires asking whether certain statements were not true, somewhat true or certainly true. These statements - which included "I am often unhappy, down-hearted or tearful" - were designed to assess whether children were at risk of various problem behaviours, including emotional problems.
Sarah Brennan, chief executive of the charity YoungMinds, said: "This research is shocking further concrete evidence of the serious and worsening state of children and young people's mental health in this country.
"Young people tell us that they feel enormous pressures today ranging from bullying, the 24/7 online environment and sexual pressures to issues around body image, school stress and family breakdown.
"YoungMinds is concerned that these are affecting girls in particular. Put this together with the lack of help available and the case for investment is undeniable."
Useful websites and helplines:
- Samaritans, open 24 hours a day, on 08457 90 90 90
- Mind, open Monday to Friday, 9am-6pm on 0300 123 3393
- Young Minds offers information to young people about mental health and emotional wellbeing
- Students Against Depression, a website by students, for students.
- HopeLine runs a confidential advice helpline if you are a young person at risk of suicide or are worried about a young person at risk of suicide. Mon-Fri 10-5pmand 7pm-10pm. Weekends 2pm-5pm on 0800 068 41 41
- HeadMeds - a straight-talking website on mental health medication
- Student Minds supports students across the UK to bring about positive change on their campuses through campaigning and facilitating peer support programmes. To join the community or launch a student group contact the charity on email@example.com