A fourth pupil at St Ambrose High School in Coatbridge has tested positive for coronavirus.
NHS Lanarkshire confirmed the latest case on Tuesday night after the student was identified as being a close contact with another affected pupil.
They had been self-isolating before undergoing a Covid-19 test which confirmed they had caught the bug.
An investigation remains underway by health officials in a bid to cut the risk of transmission amongst pupils, stuff and the local community.
One pupil at Caldervale High School in Airdrie and another at St Andrew’s High School in Coatbridge have also tested positive.
Three other people, who are not staff of students at schools in the area, have also been confirmed as having the virus and are connected to the cluster.
The total number of cases connected to the cluster now sits at nine.
Anyone with symptoms is being told to stay off school or work and urged to get tested if they have a cough, fever, or loss of taste or smell.
Meanwhile, a pupil at Carntyne Primary in Glasgow has also tested positive for the virus, it was announced on Tuesday.
