Thousands of parents are in limbo as many schools will not decide until tomorrow morning whether to open.
With pupils due back after the Christmas break, hundreds of schools are expected to remain closed because of freezing temperatures.
But many others will not decide until the very last minute whether or not to open their doors. Primary schools on rural roads which have not been gritted are the worst affected.
Individual school managements will decide whether to open their doors tomorrow.
The Department of Education said boards of management should consider issues like access and safety when making decisions about whether to open.
Eileen Flynn of the Catholic Primary School Management Association said schools should make a number of checks before making a decision on whether to open. "Our advice is that they should check ... that the school is internally operational in other words that water supply is working, heat is OK and that they can provide safe access into the school building for the children once they arrive there in the morning," Ms Flynn said.
The situation is not likely to improve in the short term as the country's most prolonged cold spell in nearly 50 years is about to get worse. A severe weather warning is in place as temperatures of -10C are forecast for the weekend.
Up to 5cm of snow was expected to fall in the east Leinster region today. The heaviest snow falls last night were in south Dublin, Wexford and Wicklow.
Met Eireann said, if anything, it will get a bit colder over the next few days. It said temperatures at night will probably be lower, with heavy showers of snow continuing in Donegal, Mayo and Roscommon.
There is a possibility of "significant" showers of hail, sleet and snow by Saturday.
Heavy snowfall in the UK has caused travel chaos for many travelling across the water.
Aer Lingus cancelled its 9am flight to Heathrow, its 9.30am flight to Manchester and its first flight to Gatwick.
"It's a very fluid situation and we're monitoring things on an hour-by-hour basis," Aer Lingus' Enda Corneille said "Our advice to customers at this point is to check the website, aerlingus.com."
Dublin Bus said it is operating a full service, though there are a number of areas in the suburbs and in industrial estates where it cannot operate. It said about 95pc of its network is operating.
Bus Eireann said the majority of its services were operating this morning, with some delays. There were some cancellations in the north Leinster area and some diversions in Cork on city-to-county services.
The 103 route did not operate between Ashbourne and Ratoath in Co Meath, the company said. In Dublin, road conditions were slightly this morning when compared to yesterday, although the suburbs and housing estates remained very icy, the AA said.
The Newcastle Road, the Griffeen Road and Chapel Hill in Lucan remained hazardous, while nearby Knockmaroon Hill was also slippery.
The Chapelizod, Islandbridge and Knockmaroon Gates of the Phoenix Park were opening today, though they remained closed early this morning.
The Department of Health and the HSE issued a warning to people to be extra vigilant.