More than 70 doctors and academics are calling for a ban on tackling in rugby matches played in UK and Irish schools.
In an open letter to ministers, they say injuries from this "high-impact collision sport" can have lifelong consequences for children.
They argue two thirds of injuries in youth rugby and most concussions are down to tackles and urge schools to move to touch and non-contact rugby.
Supporters say rugby builds character and other forms are less challenging.
The concerns have been raised as a seven-year programme headed by the Rugby Football Union is on target to introduce rugby to a million children in state schools across England.
The RFU's programme, which began in 2012 and is running until 2019, has so far reached 400 schools, with 350 to follow.
'Fractures and dislocations'
But, in their letter to ministers, chief medical officers and children's commissioners in England, Scotland, Wales, Northern Ireland and the Republic of Ireland, doctors say the risks for players aged under 18 are high.
They say many secondary schools in the UK deliver contact rugby as a compulsory part of the physical education curriculum from the age of 11.
"The majority of all injuries occur during contact or collision, such as the tackle and the scrum," the letter says.
"These injuries, which include fractures, ligamentous tears, dislocated shoulders, spinal injuries and head injuries can have short-term, lifelong and life-ending consequences for children."
The doctors say concussion is a common injury, and they highlight a link between "repeat concussions and cognitive impairment and an association with depression, memory loss and diminished verbal abilities".
One of the signatories of the open letter is Prof Allyson Pollock, from Queen Mary University of London, who has long campaigned about the dangers of rugby.
She said evidence collected over 12 years showed rugby players up to the age of 18 or 19 had a 28% chance of getting injured over a season of 15 matches.
"If you're thinking of a million children playing every year with this risk of injury you're looking at 300,000 extra injuries a year, including up to 100,000 concussions," she said.
She added that 90% of injuries resulted in more than seven days lost from school.
There are various forms of touch or tag rugby, in which tackles are replaced by touching a player or removing a tag from their clothing. Aspects of rugby such as scrums and rucks are also excluded from these forms of the game.
PE teacher's view
Jonny Cross, a PE teacher at Congleton High School in Cheshire - where rugby is compulsory from the age of 11 - says the sport provides a challenge.
Mr Cross says children wear gum-shields and are taught how to maintain the proper posture in scrums to avoid injury, a technique known as "tower of power".
"Contact rugby helps build character. They are putting their body on the line in a match. The risk factor is part of it," he says.
"They enjoy the contact element. There is a 'boy factor' - it's partly about developing masculinity. They would be more likely to be bored by touch rugby.
"I would say that some students need it. It provides a challenge, where challenge is being taken out of everyday life."
The RFU and the Welsh Rugby Union both said they took player safety "extremely seriously" but that rugby was a "fantastic sport for children" which offered many benefits for society.
The Scottish Rugby Union said it was "committed to player welfare at every level of the game" but pointed out that every sport carried "an element of risk".
South African schools allow tackling, as do schools in Australia - although there has been a recent push to make children wear protective headgear, but this is not compulsory.
In New Zealand, tackling is permitted, but in some schools it is banned in lunchtime games that are not being supervised.
Former England rugby player Matt Perry said: "I took a risk when I started rugby at seven and I'm afraid at school level if that tackle is taken out we've lost one of the great games and one of the great cultural games."
Former England international Brian Moore dismissed the evidence in the letter as "flawed" and "partial".
Obesity would kill more children than rugby, he said.
"If you want to ban things, you've got to do it on the right basis."
The Association for Physical Education said contact versions of the game should be introduced and managed only by "suitably experienced staff" following recognised guidelines.
"Parents should be aware of what sports are taught in the schools they choose to send their children to - if rugby is taught, then parents send their children to the school in the knowledge that they are likely to be asked to play rugby at some level," it added.
A spokesman for the Department for Education in England said: "Team sports, such as rugby, play an important role in developing character.
"We expect schools to be aware of the risks associated with sporting activities and to provide a safe environment for pupils."