PRIMARY school teachers are using time set aside for teaching reading, writing and maths to instead prepare children for making their First Communion and Confirmation.
Over 70pc of teachers said the preparation of children for the sacraments takes more time than is officially available for religion in their class timetable.
In some cases, an extra nine hours of teaching time a week is being used to ready children for these religious milestones.
Teachers are supposed to devote just half-an-hour a day, or a total of two-and-a-half hours a week, to religion.
However, a survey of 363 primary teachers by the Irish National Teachers' Organisation (INTO) has found that most are exceeding this allocation.
The findings of the survey will be presented at the INTO Equality Conference, discussing religion in primary school, which takes place in Limerick today.
A similar poll was last carried out in 2002 and shows dramatic changes in attitudes to the teaching of religion.
Some 49pc of respondents said they willingly teach religion – a drop of 12pc from a decade ago. Around 10pc said they would prefer to teach a broad religious education programme – double the number since 2002.
However, there was also an increase in the number of teachers who are not opposed to teaching religion – 20pc compared with just over 12pc previously.
Teachers were also asked what happens when they have a child who is of a different religion to the ethos of their school.
The vast majority (80pc) said they have pupils in their class with a different religion, accounting for anything from 1pc to 20pc of the total class.
In some schools, these children participate in the full religious programme and sacraments, while in others they take part only in the religious programme. In other instances, children are given other work to do or follow their own religion programme.
Anne Fay, president of the INTO, said the findings show the need to accelerate reform in the education system.
"It is more than a decade since the INTO called for more diversity in the system yet to date there has been minimal change.
"Parents are the primary educators of their children, yet when it comes to sacramental preparation, many teachers report that parents leave it to the schools," she said.
Ms Fay said teachers want to see parents more involved in this area.