Tens of thousands of pupils in Northern Ireland have done virtually no schoolwork since lockdown began in March, a major study has found.
Researchers at the University College London's Institute of Education said pupils across the UK had been studying an average of just 2.5 hours a day - much lower than previously thought.
Around 2.3m pupils were estimated to be doing one or less hours of school work a day.
Although Northern Ireland was not the worst-affected region, the study showed that 16% here were still in this category - or around 55,000 primary and secondary school pupils.
The study also showed that two-thirds (64.8%) of pupils were working between one and four hours a day, with just under a fifth (18.9%) studying for four hours or more.
A fifth (20%) of Northern Ireland's pupils were getting one or fewer offline lessons - such as worksheets, assignments and watching videos - a day.
Over half (54.4%) were getting one to three lessons, while a quarter (25.2%) got four or more, which is slightly higher than the UK average of 20% getting four or more.
For online lessons - such as live online lessons or meetings - the UK average is for 7% of pupils to get four or more lessons a day.
Northern Ireland had 4% of pupils receiving this, with 30% getting one to three lessons and two-thirds (66%) getting none or less than one.
Professor Francis Green, lead author of the study, said an early safe return to schools should now become a top priority for the government to stop "a potential threat to the educational development of a generation of children".
DUP MP Sammy Wilson said he wasn't surprised so many pupils were falling behind, with those in deprived areas the most affected.
He also called for a "total" return to normal school life in September, accusing teaching unions of making "excuses", and claimed the risk of pupils getting infected with Covid-19 was very small.
It comes as hundreds of teachers are due to challenge Education Minister Peter Weir this evening over safety arrangements and funding for when key school years start to return on August 17.
"It's likely that the pupils that are doing the least are the ones with the least support at home and will have other disadvantages," Mr Wilson told the Belfast Telegraph.
"It's quite clear that not everybody is equipped to teach their youngsters at home. Not every youngster has the opportunity to study at home. They might be living in crowded accommodation and not have their own private study space.
"Leaving aside the impact on the economy of parents not being able to work while children are off school, the educational disadvantage is going to build up and affect children in the long term."
He said getting schools "totally back by September" needs to be a top priority, as well as "some catch up" lessons for critical years "some time in August".
Asked about safety and funding concerns expressed by teachers, he said: "There's no reason why schools shouldn't operate as normal.
"The danger of children being infected at school is very unlikely.
"I think that teachers' unions will continue with these excuses and try to avoid going back for whatever reason."
This evening, Education Minister Peter Weir will address around 300 teachers for an online meeting hosted by the Ulster Teachers' Union.
Members are to demand assurances on funding new teaching arrangements, mental health support for pupils, on workload and assessment.
UTU General Secretary Jacquie White said members needed clarity on what the 'new normal' for schools will look like.
"How will special educational needs and assessment issues be handled and what are the workload ramifications for teachers of all this?" she queried.
"These are the issues on which we want - and deserve - urgent clarity.
"For too long the education system has been running on empty, shored up by little more than the goodwill of our profession," she added.