A staggering €19m was paid in rental costs for prefabs at our schools last year.
Schools have been forced to use prefabs for up to 14 years, while they are waiting for more permanent accommodation.
The use of prefabs has been criticised by teaching bodies for being too hot in summer and too cold in winter, with poor acoustics in some cases.
Education Minister Ruairi Quinn released new figures showing that prefab rental costs for Dublin primary schools last year were just over €4m, and €279,961 for secondary schools.
This brought the annual rental bill in the city and county to a staggering €4.2m in 2012.
After Dublin, Cork had the second highest bill – to €2.4m for primary schools alone, and €287,568 for post-primary schools, bringing the annual cost to €2.7m there.
Galway schools had the third highest bill at €1.3m, closely followed by Meath at €1.1m in total.
Figures nationally reveal that €17.4m was spent on renting prefabs for primary schools last year, compared to a much lower €1.6m for secondary schools.
The figures were released to Fianna Fail TD Dara Calleary, who sought information from the minister on the matter.
The Government announced last year that €40m had been earmarked for a prefab replacement scheme, to allow schools to proceed with the construction of permanent classrooms.
Some 194 mainstream classrooms and 105 resource teaching and learning support rooms were given the go-ahead.
The initiative to replace rented prefabs involved a total of 180 schools nationwide.
The minister said that the Government was committed to phasing out the inefficient renting of prefabs.
According to the latest figures, the cost of renting prefabs to the State fell to €19m from a total of €39m in 2009.
However, the Irish National Teachers Organisation has previously warned that: "There is a long way to go before prefabs become a thing of the past."
Meanwhile, separate figures from the Department of Education show there are hundreds of schools "currently renting temporary accommodation".