The Department of Education has raised no objection to a school holding a socially-distanced assembly of 152 pupils.
As students started to return to school for the first time in almost six months, incoming first years at St Leo's College, Carlow were welcomed with a prayer service, with pupils seated a metre apart in the hall.
The assembly sparked controversy with Association of Secondary Teachers Ireland (ASTI) president Ann Piggott describing it as "unwise and ill-advised".
Principal Niamh Broderick, whose daughter Laura (13) was among the group, said they had followed Department guidelines and everything was done properly and safely.
Ms Piggott told RTÉ that in the community "we are being told no more than 15 people can gather outside and six inside. It would be better if assemblies happened in small numbers, not in large gatherings."
In reply to queries the Department of Education did not comment directly on the event, but stated: "As part of the suite of public health measures, limits were placed on gatherings in other settings in order to support the reopening of schools which, by its nature, involves significant numbers of staff and students in school buildings."
Meanwhile, Education Minister Norma Foley will appear before the Oireachtas Covid-19 committee next week.
The minister has been under pressure to make herself available to discuss school reopening with TDs and senators and has accepted an invitation for September 2.
Ms Broderick said "the feedback from the students and parents was fantastic. Everyone complied, the children were all really superb."
"We are doing the best we can. It's great to see the children, and the staff are all so happy to be back. It's just a shame we couldn't see the children's smiling faces.
"There was of course a level of nerves and anxiety, but once everyone came back and saw the measures we have put in place, everyone feels reassured now."
Living with the threat of Covid-19 means schools will have staggered lunch breaks, minimised movement of students, a one-way system in and out, hand sanitisers in every classroom and corridor and ventilation of classrooms
Other measures include advising pupils to minimise what they bring to school and not to share items.
Pupils are receiving Covid-19 training and Ms Broderick said: "It is the nature of girls to greet one another, so we are really teaching how to maintain social distance and how to move around school in this new normal."
Patricia Pina, mother of first year pupil Jasmine (12), said she felt "much more confident" after the first day.
"Jasmine had a lovely day. She is happy and feels safe, so I feel relieved. Jasmine loves school and children need to be back together, to learn together."
Cleopatra Rammusi, whose daughter Nthati (12) has also started at St Leo's, said she felt comforted by the school giving parents detailed information beforehand.
"It went well and Nthati enjoyed her day. She is used to wearing masks, but in a class setting it was kind of weird. But she's used to wearing it so she was happy to be in school with a mask.
"I don't think parents and kids should worry. There's different opinions but if you can let your child do a sport, why not send them back to school in what is a more controlled environment?"