More than one in 10 pupils in Scotland are absent from school with attendance down to 86.7%, according to Scottish government figures.
Data collected from local authorities shows that more than 73,000 pupils were off school at the end of last week.
However, only 21,832 of the absences are recorded as “Covid-19 related”.
The Scottish government said it was common for other viral infections to circulate after a “prolonged break” away from school.
Pupils in Scotland began returning to school on 11 August after being away since March.
Provisional figures from 27 August show that 86.7% of pupils in Scottish schools were present, down from a confirmed 95.8% attendance on 17 August.
Attendance remained above 90% until 21 August, before dropping to 89.2% on 24 August following the weekend.
About 3% of pupils were absent last Thursday for a Covid-related reason, with 10.3% absent for non-Covid reasons, including pupil exclusions.
Over the last decade, attendance levels over the whole school year have been between 93% and 94%.
Covid-related absences in Scottish schools
The Scottish government reported last week that almost 17,500 children had been tested for coronavirus, but only 49 cases had been detected.
Speaking on Monday, Education Minister John Swinney said it was common for “colds and similar viral infections to circulate” when pupils returned from a prolonged break.
“In many cases children will be well enough to attend school and continue their learning with little or no interruption to their education,” he said.
“In other cases, for instance where they have quite a heavy cold with a runny nose, they may need to take a day or two off to recover.”
He said any pupil with Covid-19 symptoms were required to self-isolate and seek a test.
But he added: “In order to ensure that your child does not miss out on their education it is important to be clear on how Covid-19 symptoms differ from those of other infections that we normally see circulating at this time of year.”
Attendance in Scottish schools
National clinical director Jason Leitch has also written to schools with guidance on what to do about pupils who develop non-Covid symptoms.
The Scottish government said a Covid-related absence included a “positive test, showing symptoms, self-isolation, quarantining, and parents not sending their child to school against public health guidance”.