Religious-run secondary schools in Ireland are more likely to receive voluntary contributions from parents.
The level of payment they receive is also likely to be higher than in the case of non-religious schools, according to a report by the Economic and Social Research Institute.
The report finds what it calls "stark differences" in the level of parental contributions received.
It quotes one school manager who talks of some schools requesting as much €600-€700 from parents.
There are three kinds of second-level schools in Ireland: voluntary or religious-run schools, vocational schools and community or comprehensive schools.
The ESRI report was commissioned by some of the trusts that run the Catholic voluntary schools.
It found that voluntary schools are much more reliant on parental contributions, with almost 90% receiving contributions.
That compares to just over 60% of community and comprehensive schools, and half of all vocational schools. The amount requested also differs significantly.
One in five religious-run schools looks for €200 or more per year.
One in three looks for €150 or more.
Schools in the other sectors generally ask for between €50 and €74.
This report questions the reliability of voluntary contributions as a source of basic school funding at a time when many families have less money.
The report finds State funding to schools is distributed through very different mechanisms, according to the type of school.
It says for this and other reasons it is not possible to compare levels of State funding between the sectors.
It also says while voluntary schools are believed to receive less, the facts are difficult to establish.
The report, called Governance and Funding of Voluntary Secondary Schools in Ireland, recommends a more transparent system of financial allocation.
The report makes a number of other findings, among them that voluntary schools are more likely to be oversubscribed and are more likely than other sectors to have middle class and higher-ability students.
Voluntary schools are also far less likely to be classified as disadvantaged - 12% versus 57% of vocational schools.
The report also finds that 12% of overall income in voluntary schools comes from parents, compared to between just 5% and 6% in other post primary schools.
It finds that many schools across all sectors have introduced changes in the past year, some as a result of reduced funding.
More than one third have dropped one or more subjects.
One in ten has dropped the Leaving Certificate Applied Programme, 3% have cancelled Transition Year and 7% have increased the parental contribution.
Religious run schools are privately-run but publicly-funded.
This report was commissioned by a number of Catholic school trusts to gather information to be considered in drawing up new models of funding their activities.
These trusts were established in recent years by the religious congregations to run their schools and do not get State funding.
The report highlights concerns felt by the trusts about the sustainability of current funding mechanisms into the future.
Drawing on international comparisons, the report concludes that any additional funding provided by the State may have to be matched by a ceding of control on the part of trusts on issues such as the appointment of teachers or school admission policies.