Millions of pupils have returned to classrooms in England and Wales, amid fears of a spike in Covid cases.
Pre-term Covid testing is being used to limit infection, but rules on social distancing and face masks have gone.
Ministers want a return to normality, but cases are more than 30 times higher among children compared with last year.
In the week to 28 August, there were more than 300 Covid cases per 100,000 among five to 15-year-olds. This compares with less than 10 per 100,000 in the same week of 2020.
Head teachers are hoping for a much smoother term but also want school safety measures to be kept under review.
Geoff Barton, head of the Association of School and College Leaders, says there is less uncertainty about how the coronavirus may impact on schooling, but he wants the government to be ready to "step in with support" if needed.
First day back: 'Not complacent'
Katie Scarnell, principal of Greensward Academy in Hockley, Essex, has had a very busy start to the new school year - welcoming back all pupils for the first time.
The secondary school head is "really pleased to be back and it's great to have the school back to some level of normality for the first time in a long time".
Although most of the safety measures have been eased in schools, Mrs Scarnell isn't worried. "I think the big thing is we're not complacent about it."
At Greensward Academy they will still have hand sanitisers in every classroom and staff have been told to be vigilant about ventilation.
She thinks the issue of vaccinating 12-15 year-olds should be left to the medical experts, but says: "I would be concerned if parents' consent for of 12-15 year-olds is not required. I think parents' consent is definitely needed for children that age."
One her pupils, Emma, aged 13, is starting her third year - and she has a mix of excitement about being back and worry about the learning she's missed.
"My year hasn't done a full year at secondary school yet. We've had about the half of the time doing online learning and a third of it for Year 8. Hopefully, there won't be any lockdowns or isolation this time," she says.
Emma doesn't think Covid will go away, she says: "I think we will just have to live with it."
Although health officials are clear young people are likely to have milder symptoms from Covid, there is still anxiety among some pupils about how the term will work out, after 18 months of intermittent disruption.
Bournemouth A-level student, Olivia - a member of the NSPCC's young people's board for change - says she finds the prospect of just carrying on "very daunting" and has asked if she can repeat last year.
"We're being dropped back into this new normality, where you're meant to be applying to university and sitting your A-levels as if nothing has happened," says the 17-year-old.
Modified exams have been pledged in all four nations, but there is little detail yet on England's plans for these, and pupils and teachers are asking for more information.
National Association of Head Teachers general secretary Paul Whiteman said schools were focused on helping pupils recover from the disruption.
But he added there were ongoing concerns around the level of support offered by the government and more funding was needed to ensure pupils get what they need.
A Department for Education spokesman said this term's safety measures strike a balance between making schools safe and reducing disruption.
"We know the past 18 months have been incredibly difficult for young people, and we have invested more than £17m to build on the mental health support currently available in schools."
The NSPCC says concerns over the school return were a frequent theme during its ChildLine counselling sessions this summer.
Between the end of June and 16 August it delivered 441 counselling sessions related to going back to school or college.
One 14-year-old anonymous caller to the helpline, whose sister is clinically extremely vulnerable, said: "I haven't been to school much over the past two years.
"It's quite scary to think that... I'm going back to school full-time and the rules on masks and social distancing have been eased."
Northern Ireland GCSE pupil, Aoife, is worried about school work. As a second year GCSE student she would have completed most of her exams by now.
'Home is not the same'
Aoife struggled working from her bedroom during lockdown and says: "Even coming home now, it feels different to how it did before Covid."
She has found it particularly hard to deal with not knowing what is going to happen next.
"It's horrid when you don't know if the decisions that are being made for you are the best or just the easiest at the time," she adds.
Some schools across England, Wales and Northern Ireland have already opened their doors to pupils - some to offer Covid testing or to start lessons.
Blackburn pupil Muhammad Sahal, 14, also an NSPCC board member, is looking forward to seeing friends and getting back to his studies.
He worries about the face-to-face teaching he has missed and says there has not been "much normal during my time at secondary school".
"It's great that the school bubbles have gone, however there are concerns such as the rise of Covid cases in Scotland."
Schools in Scotland re-opened mid-August, as usual, and this led to a faster rise in Covid cases despite social distancing measures staying in place.
Scotland, schools and surges
By Christine Jeavans, data journalist
What can the pattern of Covid cases in Scotland tell us as England's schools open their doors to millions of pupils?
Most Scottish schools went back in mid-August and since then Covid cases in Scotland have reached record levels.
We can't say that the rise has been solely caused by schools returning - the increase in cases began in early August. But it then took a steeper turn while pupils were still on holiday.
The rise was initially fastest among 15 to 19-year-olds and by 20 to 24-year olds.
But cases among the under-15s in Scotland have trebled since school restarted.
Although cases were much lower at this point in 2020, they followed a similar pattern, rising before schools went back and then increasing more steeply later in September.
In England, cases have been fairly flat across August - the question is: Will the new term cause them to rise in the same way?