The uptake has been described as "impressive".
12 to 15 year olds are receiving Covid-19 jabs in most vaccination centres today and tomorrow.
More than 75,000 12 to 15-year-olds have now registered to receive a Covid-19 vaccine.
Public health expert, Gabriel Scally, is impressed with the take-up.
"Young people and their parents are very enthusiastic. They've seen the disruption Covid produces in their education," he said.
It comes as clinics throughout the country are administering first doses of Pfizer and Moderna vaccines to this age-group today and tomorrow.
Registration opened on Wednesday evening, and the first appointments started yesterday.
Meanwhile, vaccinated pupils won't need to get a Covid-19 test or restrict their movements if they become a close contact in school.
The HSE's planning the exemption as long as they don't have symptoms.
But, unvaccinated children will need to take time out of the classroom.
