A total of 27 coronavirus cases, most of them adult staff, have now been linked to a school in Dundee.
Kingspark School was closed last Wednesday as pupils and staff were asked to self-isolate for 14 days.
NHS Tayside said in an update on Monday that 21 staff, two pupils and four community contacts had tested positive.
Two other school sites in Dundee have also been identified as result of contact tracing connected to the Kingspark outbreak.
A primary two class at St Peter and Paul's School has been asked to self-isolate until 2 September after an individual tested positive.
Children who attended the Happy Times out-of-school club at Downfield Primary School are also being asked to self-isolate until the same date following a positive test result.
Elsewhere, two classes at High Blantyre Primary School in South Lanarkshire are self-isolating after two pupils and a staff member tested positive.
NHS Lanarkshire said there was no evidence to suggest transmission within the school and the school will remain open.
Kingspark School in Dundee, which has about 185 pupils aged between five and 18 who have additional support needs, was closed on Wednesday evening to allow deep cleaning to be carried out.
The decision was taken to shut it for two weeks because of the complex health conditions of the pupils.
Pupils and anyone who lives with them who cannot maintain physical distancing have been asked to self-isolate for 14 days.
Dr Daniel Chandler, of NHS Tayside, said: "Due to the high level of tests undertaken among staff who work at the school, we may see a small rise in the number of positive cases as these results come through.
"The actions and measures that have been put in place will help to prevent any further spread of infection and we hope to see the numbers of positive cases tail off over the coming days."
Paul Clancy, executive director of Dundee City Council's Children and Families Services, said: "I would like to reassure families that this action is being taken to keep everyone safe. This is our paramount concern and we cannot be complacent."