UK teenagers are less happy with their lives than those in many other nations, including the US, Germany and Latvia, an international report has found.
It puts the UK 38th out of 48 countries in terms of youngsters' life satisfaction.
Students from the UK were also much more likely to face exam anxiety and to report that they have been bullied than the global average, according to the latest report by the Organisation for Economic Co-operation and Development (OECD).
The study - based on the OECD's Programme for International Student Assessment (Pisa) tests, which are taken by 15-year-olds around the world - shows that the UK is lagging behind internationally in terms of young people's social and emotional lives.
It found that, on a scale of one to 10, British pupils had an average satisfaction of 6.98, compared with the OECD average of 7.31.
This puts the UK behind nations such as France (7.63), Germany (7.35), Spain (7.42) Latvia (7.37) and the US (7.36), but ahead of others such as Japan (6.80) Turkey (6.12) and Korea (6.36).
Among those with the highest ratings were Mexico (8.27) and Finland (7.89).
Overall, the UK took 38th place for life satisfaction, out of 48 OECD countries, and partner nations. Among OECD countries alone, it was 23rd out of 28.
Only 28% of UK students were "very satisfied" with life - short of the 34% OECD average.
Around 540,000 students took part in the latest Pisa tests, representing around 29 million 15-yer-olds in 72 participating countries and economies.
The findings also show that British pupils' time at schools is more regularly marred by bullying, with almost a quarter of British students (24%) having fallen victim to any type of it.
This figure is 5% higher than average, according to the research.
Where bullying was rife, performance was affected, as schools in which more than one-tenth of pupils fell victim to it scored an average of 38 points lower on science than schools with the lowest episodes, the study found.
Anxiety was also found to be permeating the British classroom, where 72% of students reported worrying about tests even if they were well-prepared, compared with 55% on average.
Just over half (52%) also said they became very tense during their studies, above the 37% international mean.
But the reported lack of happiness teenagers have in British schools is offset by their high ambitions, the report found.
The vast majority of pupils (90%) claimed they wanted to be the best in their every endeavour, dwarfing the 65% international average.
Similarly, 76% said they wanted to be the best in their class, outstripping the 59% average.
Confidence appeared to spell better results - as students in the top quarter of the report's motivation index achieved an average of 29 points higher in science than those in the bottom quarter.
UK teenagers also have a high level of support from their parents, with 93% saying that their mothers and fathers encourage them to be confident, and 84% saying their parents are interested in what they do at school.
A Department for Education spokeswoman said: "These findings show young people have the motivation and desire to go as far as their talents can take them and that their parents are supporting them throughout their time at school."
This report follows two volumes of Pisa results for 2015, released last December.
They found the UK's teenagers are continuing to lag behind their peers in countries such as Singapore, Japan and tiny European nations when it comes to science, maths and reading.
It found Britain made little progress in these core areas in three years.
The findings also show that nearly a quarter of UK students (24%) say that on a typical weekday they use the internet for more than six hours a day, higher than the OECD average of 16%.
Youngsters who spend more than six hours online are less satisfied with life, the study found.
Barnardo's chief executive Javed Khan said: "These findings highlight just how vital it is for children to have someone who believes in them.
"A caring home is essential to children's well-being and children themselves have told us that having someone to love, listen to, support and trust them is vital for them to lead happy lives."