Education Secretary Gavin Williamson has said keeping schools open in England is the "best course of action", despite fears about the coronavirus.
It comes as blanket school closures are being announced in European nations such as Spain, France and Ireland.
He told a head teachers' conference in Birmingham that sending all pupils home would put a big strain on key workers who would also have to stay at home.
School leaders agreed keeping schools open was the right decision.
Geoff Barton, head of the Association of School and College Leaders (ASCL), which is meeting for its annual conference, said head teachers would authorise absence if parents took the decision to keep their children off lessons.
He anticipated absences would be small in scale and similar to "snow days".
The government has said individual schools may be advised to shut by Public Health England if necessary.
Mr Barton said there was pressure from parents for more information and guidance about what might happen to national exams.
The exam season starts in early May, when the virus outbreak is expected to reach its peak, but exam regulators are urging schools to prepare for public exams as normal.
GCSE exams start in the second week of May and run until mid-June.
Mr Barton said many head teachers were facing questions about the exam season, and there was an urgent need for reassurance.
"Parents and pupils are worried about being the victim of something out of their control and are asking, 'Will I get into college or university?'"
Mr Williamson said: "We're doing everything we can to make sure it's fair for students, we're having regular discussions with Ofqual."
The government warned on Thursday that within weeks, whole households would be asked to self-isolate if one person showed symptoms consistent with coronavirus.
It is not clear exactly what this would mean for a teenager unable to sit their exams, but there are mechanisms for allocating marks in exceptional circumstances, which have been used before.
The Welsh government has been advised that school closures are not an appropriate move at the moment, though the situation remains under review.
The Scottish government has also said school closures would not be an effective measure at this stage.
The Republic of Ireland's decision to close schools, colleges and public childcare facilities until 29 March is likely to affect businesses in Northern Ireland's border region that employ staff from the Irish Republic.
In the meantime, many schools will continue to assess how technology could be used to continue pupils' learning in the event of isolated closures.
Sharon Bruton, chief executive of the Keys Federation Academy Trust in Wigan, whose schools use an artificial-intelligence learning platform, said teachers could set assignments via email and social media accounts.
"Schools are adaptable and flexible places - I'm certain school leaders and curriculum leaders will be thinking about how teaching can continue for their students should this be an eventuality," she said.
"Educators are remarkably resilient and adaptable and I think part of our job is to meet the needs of our children and make sure they can thrive in challenging circumstances - and this [coronavirus outbreak] won't be any different."
So the possibility of blanket school closures has been kicked down the road, but that doesn't remove the uncertainty entirely.
No head teacher can rule out the possibility their school could be affected at some point. More pressing is the likelihood that the peak in cases could coincide with exams due to begin in mid-May.
This might mean more households isolating, more teachers off work.
One option could be to move some exams to later in June, when fewer are traditionally scheduled to take place.
This would prolong the agony for teenagers, and their families, but could increase the chances of most being able to sit the exams that are the passport to the next stage of their life.
In the meantime, despite expert advice, some parents continue to call for school closures.
The exams watchdogs for England, Scotland, Wales and Northern Ireland are all urging teachers and students to prepare for the exams season as normal.
In Scotland, where exams start earlier than the rest of the UK, the Scottish Qualifications Authority said there was no change to the 2020 national-qualifications timetable.
"Current deadlines for coursework, and other assessments, remain in place," it added.
England's exams watchdog, Ofqual, said: "We continue to work closely with exam boards, other regulators and the Department for Education and we have met to plan for a range of scenarios, as the public would expect.
"Our overriding priorities are fairness to students this summer and keeping disruption to a minimum."
Qualifications Wales said: "We will provide guidance on our website to reflect any specific arrangements that schools and colleges should put in place if required."
Northern Ireland's Council for the Curriculum, Examinations and Assessment (CCEA) said there were "a broad range of contingencies to ensure the smooth operation of examinations", which would be updated if necessary.
"In the meantime, students, schools and colleges should continue to prepare for the summer examinations and assessments as usual," it added.