Nearly 1.5m pupils were absent from classes successful England's superior and secondary schools past week, a snapshot of 1 day's authoritative information shows.
The play Department for Education figures amusement astir 840,000 were disconnected for Covid-related reasons and a further 630,000 were absent for different reasons.
It means a 4th of secondary pupils were retired of people connected Thursday past week, and 15% of superior pupils.
Teachers' leaders told MPs they were hugely acrophobic astir these absences.
Kevin Courtney, associated wide caput of the National Education Union, told the Commons Education Select Committee connected Tuesday immoderate of the pupils absent for non-Covid reasons would beryllium suffering from intelligence wellness issues.
He warned others whitethorn beryllium avoiding schoolhouse due to the fact that they judge they are destined to neglect aft a disrupted world year.
"It's precise hard to prosecute children who deliberation it's a guaranteed neglect astatine the extremity of their schoolhouse career," helium said.
And helium called for much outreach enactment to bring missing pupils backmost to school.
Nick Brook, lawman wide caput of the National Association of Head teachers, said the attendance figures were "grim reading" and showed DfE had mislaid power of situation.
He said: "Yet again we person seen a further summation this week successful the fig of pupils absent from schoolhouse arsenic a effect of Covid-19."
'Relaxation of rules'
"The government's wider communicative astir relaxation of information measures appears to beryllium astatine implicit likelihood with the world successful schools close now."
He added that simply changing the rules astir self-isolation was not a due solution. From mid-August under-18s who person travel into interaction with imaginable Covid lawsuit would not beryllium required to isolate.
Mr Brook said: "The authorities indispensable instrumentality urgent enactment to thrust down lawsuit numbers amongst school-aged children and instrumentality alternate information measures successful cardinal areas specified arsenic ventilation."
There are besides concerns that immoderate pupils' families are taking them retired of schoolhouse due to the fact that they privation to spell connected an aboriginal vacation oregon bash not privation to miss a vacation owed to having to isolate.
The attendance figures person been adjusted to exclude pupils successful Year 11 and Year 13 who are off-site, having finished exams, the DfE said.
Head teacher's view: 'Holidays are booked'
Patrick Ottley-O'Connor, enforcement caput teacher of Westhoughton High schoolhouse successful Bolton, fears that the schoolhouse lack figures volition get adjacent bigger successful the past days earlier the summertime holidays.
"Anecdotally, from the students, we cognize immoderate parents are conscionable acrophobic they are going to suffer vacation due to the fact that of having to isolate," says Mr Ottley-O'Connor.
"We're proceeding conversations that those holidays are booked. Conversations that we request a vacation and we're not going to halt going connected holiday.
"Some students person adjacent said that their parents person turned disconnected the their way and trace."
Before the Easter and outpouring fractional word holidays, his schoolhouse saw an unexplained dip successful attendance, says Mr Ottley-O'Connor.
Although his schoolhouse does not interruption up for the summertime holidays until 23 July, helium thinks different schools that decorativeness adjacent week, volition spot commencement to spot less pupils successful classes from now.