More than 3,000 school pupils are SLOT XO isolating across north-east Wales, councils have said.
Wrexham council reported about 1,900, Flintshire council about 1,100 and Denbighshire council said it had eight primary and four secondary schools with pupils isolating.
In north-west Wales, Conwy council said 18 schools were affected and Gwynedd council said 11.
The north currently has Wales' highest Covid case rates.
In Flintshire, 142.9 people per 100,000 population tested positive for the virus for the seven-day period leading up to 23 June.
That is followed by Denbighshire with a case rate of 104.5 and Wrexham on 91.2.
Wales' overall case rate is 53.1.
Flintshire's chief officer for education and youth service Claire Homard said since 21 June the county had seen 60 new Covid-19 cases across 24 schools, but there were no current plans to close any schools in response.