Fiona McAlinden of Our Lady’s Grammar School said parents were "gracious and understanding".
"It has been clear to me and many other school leaders, since before Halloween, that schools should have moved to remote learning on December 11 to avoid this scenario, but our voices were not listened to," she said in a social media post.
"How can it not be obvious that schools should deliver remote learning for the first fortnight in January?" she asked.
"Exceptions could be made for P7s and Year 12s, so that the transfer test and GCSE English and maths modules could go ahead, but limited numbers would reduce risk for everyone."