I assume that the Deputy is enquiring about tax relief on tuition fees (including the student contribution) for which relief is available.
Data relating to the tax relief for tuition fees is available on the Tax Expenditures table available on the Revenue Statistics webpage (www.revenue.ie/en/about/statistics/costs-expenditures.html). This shows the estimated number of applications and cost to the Exchequer of relief in respect of qualifying third level education fees.
When tax measures are introduced or amended, an estimate of their cost in the first and full year are generally calculated. Such estimates would be influenced by the numbers of students and qualifying courses, as well as the income tax liabilities of those paying the relevant tuition fees in the tax year concerned. Therefore, the scheme is demand led in nature and the cost fluctuates accordingly.