Children in third class and above have to wear masks in school from today onwards.
New Department of Education guidelines state a medical cert's required for an exemption, and those without evidence will be refused entry.
The government's also calling for less indoor socialising among under-12s for the next two weeks, after a sharp increase in Covid cases.
There were over 18,200 among under-18s in the fortnight to Sunday - compared to just over 13,700 in the previous two weeks.
Nearly 123,000 Covid cases were reported last month - which is 17 per cent more than the previous peak in January.
The government fears a further spike due to the Omicron variant - leading to more restrictions.
From Friday, people arriving into Irish ports and airports will need a negative PCR or professionally conducted antigen test.
