A fifth case, linked to young people but not attending school, has also been identified.
One of the pupils from St Ambrose “was present at the school for about 20 minutes”, according to NHS Lanarkshire Director of Public Health Gabe Docherty.
He also said the St Andrew’s pupil “attended school for a relatively short period” on Thursday before testing positive on Friday.
Mr Docherty said: “The first student from St Ambrose tested positive on August 13, after showing mild symptoms since August 11.
“A second student, a close contact with the first outside the school, also tested positive yesterday. Neither went to school.
“The third student from St Ambroise, a close contact of the other two outside the school, tested positive this morning (August 14) and was present at the school for about 20 minutes yesterday (August 13).
“This student had limited contact with other students while in school during this time. The student was immediately isolated and taken home to self-isolate for 14 days.
“The student at St Andrew’s tested positive this morning (August 14) and had been in school for a relatively short period yesterday, with limited contact with a defined number of individuals, hence the risk to them. other students and staff was rated as very slow. “
None of the cases had serious illness.
Mr Docherty added: ‘NHS Lanarkshire is working closely with the North Lanarkshire Council regarding these cases and quickly identified close contacts in both cases.
“Public health advice is given to these people and they are told to self-isolate.
“Our Testing and Protection service will continue to contact anyone who may be affected and, following the findings of a review this afternoon, the risk to the school community as a whole is low.
“The incident management team continues to meet daily and strong contact tracing continues. ”
Dr Jennifer Darnborough, NHS Lanarkshire consultant in public health medicine, also said: “The team is investigating any potential connection to the wider community that has an impact on schools.
“There is evidence that mixing socially in the community without maintaining physical distancing measures can transmit the virus.
“It should be noted that, given the current situation, there is currently no evidence to suggest transmission in schools, but people are urged to remain vigilant and practice physical orientation from a distance.
“We are aware that there will always be concerns among children and their parents at this time. I can reassure them that all the settings that these people frequented during their infectious period are being identified and evaluated.
“Individuals should stay out of school or work and get tested if they have symptoms of Covid, such as a cough, fever or loss of taste or smell, even if they are light. Information on how to access the tests is available from NHS Inform.
A Scottish government spokesperson said: ‘We know that a small number of pupils at two schools in Coatbridge have tested positive for Covid-19.
“NHS Lanarkshire has made it clear that there is currently no evidence to suggest transmission in schools and NHS Lanarkshire is currently conducting a community-wide investigation.
“NHS Lanarkshire is also taking appropriate action by writing to parents at the school to offer them the comfort and detail steps it is taking to deal with these cases. ”
It comes after another group in north-east Glasgow has been linked with a number of students at Bannerman High School in Baillieston.
The NHS Greater Glasgow and Clyde said there was “no indication that transmission has occurred in the school” and that none of those affected returned to the classroom when it reopened.