Pupils are being urged to take a rapid COVID-19 test before returning to school after half-term, as it emerged that fewer youngsters have been vaccinated than previously thought.
Latest figures show that coronavirus cases among 10 to 19-year-olds are currently the highest of any age group, with a weekly rate of 1,201 per 100,000 population.
The UK Health Security Agency (UKHSA) and ministers are calling on secondary school and college students to have a lateral flow test to identify hidden asymptomatic cases and prevent COVID-19 from entering the classroom.
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In the run-up to Christmas, they say it will help to minimise disruption to lessons and ensure families can "enjoy the best" of the festive season.
Secondary school and college students in England have been asked to test twice weekly at home since returning to class in September.
People with symptoms should isolate and take a PCR test.
Health chiefs have also stressed the importance of young people being vaccinated, with jabs now available through both schools and walk-in centres.
After vaccines, rapid testing and isolation where necessary was the most important way to break chains of transmission, especially as the country enters winter, they said.
However, a change in official counting methods to improve the accuracy of figures reveals thousands more eligible under-18s have not been jabbed in England.
The revised UKHSA estimate shows just 19.3% of 12 to 15-year-olds have been vaccinated, compared to the 22.1% previously reported, according to The Times.
In Scotland, 53.1% of this age group have been vaccinated.
UKHSA chief executive Dr Jenny Harries said: "Today I am calling on all children to help themselves and each other by getting tested before going back to the classroom so that we can stop the infection in its tracks and keep as many children in the classroom as possible, continuing their education and developing their futures."
Education Secretary Nadhim Zahawi said: "As we start the countdown to Christmas, testing regularly and getting vaccinated is the best thing we can all do to protect education and make sure we can enjoy the best of the season - whether that's the school nativity or the family gathering over the holidays.
"That's why I want to encourage every young person in secondary school or college to take a test before you return to the classroom next week.
"We have come so far in our fight against this virus, and now every single test and every single jab puts another brick in our wall of defence."
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Health Secretary Sajid Javid said: "As students prepare to go back to school and college after half term, it is vital that they are taking free and easy rapid tests that will help detect COVID-19 infections from those who are not showing symptoms to keep the virus at bay.
"Alongside testing, the vaccines are a huge defence in our armoury."
Meanwhile, Wales' first minister, Mark Drakeford, said he is having to reimpose some COVID restrictions due to rising cases.
