Social distancing in schools could be almost unmanageable, a headmaster in Northern Ireland warned.
A limited number of pupils are expected to return to classes in August.
A rule that people stay two metres apart is intended to limit the spread of coronavirus.
There is a growing sense in the community at large that young people are perhaps those with most to lose following this pandemicStephen Black, Ballymena Academy headmaster
Stephen Black, headmaster at Ballymena Academy in Co Antrim, said: “Social distancing is going to be very difficult to achieve.
“It would nearly be unmanageable for schools if it is as strict as that.”
“Much more of our delivery will be online than if those requirements were to be reduced.”
Mr Black is a committee member at the Association of School and College Leaders.
He told Stormont’s education committee that clear direction was needed by mid-June on issues surrounding reopening.
They could accept pupils preparing for exams in the third week of August, education minister Peter Weir has said.
Mr Black said as much clarity as possible was essential to enable principals to gauge how many young people can be safely allowed in.
“It is very clear to us that it will be impossible for all the normal content in all the normal subjects to be taught to all the populations in the normal way, given the amount of time that pupils have missed from school.”
He expressed concern that youngsters would feel anxious about the amount of material they had missed, and said harm was being caused by ongoing restrictions.
“There is a growing sense in the community at large that young people are perhaps those with most to lose following this pandemic.
“They could be the unwitting victims of this.”
He urged a cautious approach, while allowing pupils to return at the earliest possible point.