More than 100 pupils from Scottish schools have tested positive for coronavirus since classes returned earlier in August.
SNP education boss John Swinney told MSPs in the Scottish Parliament that 127 pupils across all age groups had tested positive for COVID-19.
It comes as a number of schools have told pupils to self isolate in Edinburgh and Fife after classmates caught the virus.
John Swinney said 77 pupils aged between 12 and 17 tested positive.
40 pupils aged five to 11 received a positive result.
But he pointed out well over 10,000 young people in the 12 to 17 age bracket had a negative test returned, meanwhile 28,664 pupils aged five to 11 were negative.
The education secretary told MSPs : "Full contact tracing is undertaken in all cases where a positive case is detected, and I pay tribute to the enormous industry that is put into this effort by the contact tracers."
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He added: "On the evidence that I have seen, most of the contraction of the virus is coming within household settings.
"That's not in every case, but I would say that is the predominant explanation, is in household situations and that may also be informed by international travel, which is resulting in quite a number of the cases with which we are wrestling."
