Tens of thousands of young carers in Wales are not known to schools or local authorities - putting their life chances at risk, a charity has said.
Carers Trust Wales found up to 400% more young carers than expected at eight schools in a pilot study.
The charity said those affected miss about 48 days of school a year, get fewer GCSEs on average, and sometimes faced bullying.
The Welsh education watchdog Estyn is set to review the issue.
But the charity said more money is needed to support local service.
Kate Cubbage, for the trust, said for many young people a caring responsibility can be positive - developing skills and experiences "others don't have".
But it can also affect attainment and attendance at school, she warned.
"It can impact on their grades, their life chances in terms of going on to further education, as well as their mental health and self esteem," she said.
"More needs to be done to make sure local authorities and schools work together… to identify what they need to overcome their challenges."
Stuart Gumm had a serious mental breakdown about four years ago.
Diagnosed with anxiety and depression, he often suffers panic attacks, no longer drives, and rarely leaves the house.
The 52-year-old from Talywain, in Torfaen, said the care provided by his son Carwyn, 12, has saved his life.
"It's a continuous fight against something that controls my mind, really," said Mr Gumm.
"I could quite happily leave this world on those dark days, and if it wasn't for him and my family, I would."
"That's why he's so special and why I love him so much. He recognises what's wrong, where no one else does, for a start.
"He recognised those darkest moments in me and gives me that extra will to fight, to carry on."
For Carwyn, talking about his father's illness is difficult - and he said he does not really understand why everyone thinks what he does is a "big deal".
"That I just feel that he isn't acting as normal, so I think to myself 'Something's not right here'," he said.
"I want him to feel better. Sometimes I try to forget about it, but it's not that easy."
According to the trust, official figures show there are 7,000 young carers in Wales but new research suggested there could be more than four times that number.
"We believe there could be tens of thousands of young carers that haven't been identified with schools or local authorities and there's potential to do more to identify them," said Ms Cubbage.
"In particular it's important that there's sustainable funding for local carers services to work with carers and their families."
She added that there was no reliable data on how many carers there might be, because identification is so difficult.
"The risk is that we miss the opportunity to make a difference in the lives of tens of thousands of young carers," she added.
Ms Cubbage hopes a review by Estyn will help to identify more youngsters affected so support services can be put in place for them.
A carers' identification card will also be created, with the Welsh Government set to provide £36,000 to the trust over the next year to help carers.