An initial Covid infection among pupils has a "much greater impact" on teachers when it happens in primaries than for secondaries, new analysis suggests.
This may be because primaries are "much smaller", making social distancing "harder", or because primary schools have "far fewer staff", therefore reducing scope for "coping and redeploying" them, according to the FFT Education Datalab think tank.
A "lack of investment in spatial and staffing flexibility" may therefore have led to "significantly more lost learning", it says.
Staff absence: 20,000 teachers off for Covid-related reasons
The research, published today, shows that Covid-related teacher absence rates averaged around 4.7 per cent for primary schools and 4 per cent for secondary schools for a period since the October half term.
By contrast, pupil absence for the same period was higher in secondary schools at 28 per cent, compared with 15 per cent in primary schools.
"So here is the first puzzle: teacher absence is higher in primary schools while pupil absence higher in secondary schools," the report says.
The analysis also found "very different rates" of teachers sent home by their school because of close contact with a confirmed case on site.
"This reaches over 3.5 per cent of teachers in primary schools, twice the level of the peak in secondary schools," the report says.
The think tank therefore suggests that "the (lower) pupil infection rate in primary must have a much greater effect on the number of teachers being sent home than the same rate would in a secondary school".
It gives several potential reasons for this.
"Primary schools are physically much smaller than secondaries, so social distancing strategies for teachers (and pupils) from pupils must be harder," the report says.
"Second, it may be harder for teachers in primary (and special) schools to maintain social distance from pupils. Third, primaries have far fewer staff, and are organised differently, so this must reduce scope for coping and redeploying staff.
"This seems to us to be the key new fact emerging from this data: the much greater impact that an initial infection in a primary school has on teachers isolating than in secondary schools."
The report concludes: "The difference by phase between pupil absence and teachers sent home to isolate suggests that quite a substantial fraction of pupil absence in primary school may be due to the greater effect of pupil infection on teacher absence.
"The lack of investment in spatial and staffing flexibility may have led to significantly more lost learning."