Parents are paying between €20 and €30 an hour on grinds for children as young as 11 to ensure they get the secondary school place they want, a parents' lobby group has said.
In a sign of the increasing exam pressures placed on pre-teens, the National Parents' Council (primary) said some parents were seeking extra tuition for their children before second-level assessment exams.
While it is illegal for schools to operate entrance exams, Ms Fionnuala Kilfeather, chief executive of the group, said it was not uncommon for schools to operate "de facto" entrance exams.
"Naturally parents want their children to do as well as possible ... but some schools are seen as more desirable by some parents," she said. "They are not allowed to have entrance exams, but that is not stopping them."
Parents frequently do not have access to the results of these exams.
Ms Kilfeather's office has also received calls recently from parents concerned that their children's entire second-level progress might be determined by such tests.
This was because some schools used assessment exams for streaming purposes, she said. Frequently, the exams also contained material which was not on the primary curriculum.
"It can be very difficult to get out of a lower class once the decision is made, so you are making judgments on a child's ability at a very early age," she said.
As a result, parents anxious to ensure their children perform as well as possible have contacted the NPC office to ask where they can get grinds for their children.
"It's a significant stress on children too at a time of transition from primary level," she said. "It has a very negative effect on learning ... we need to foster skills rather than make assumptions."
A spokesman for the Department of Education yesterday said it did not advocate grinds for children seeking to enter second level.
However, parents had the right to choose to send children for extra tuition if they so wished.