Up to 65,000 Leaving and Junior Cert students are taking private grinds at a cost to their parents of up to €50 per hour, according to new figures.
The survey indicates that in excess of 35,000 Leaving Cert students and up to 30,000 Junior Cert students paid for grinds outside school time last year.
Maths, where failure rates of over 10 per cent have been evident in recent years, is by far the most popular grind subject. French and Irish are the other most popular subjects.
This year's Leaving Cert results will be available next Wednesday.
The unprecedented boom in grinds is evident across all second-level classes; some 55 per cent of fifth years take grinds, while an increasing number of first years - aged 12 and 13 - are also paying for private tuition.
Grinds are much more popular among female students - even though girls now outperform boys in virtually all Leaving Cert subjects.
On average, Leaving Cert students are taking grinds for 2.5 hours per week.
The survey of some 1,000 students was conducted by Student Enrichment Services, which provides study skills courses in over 300 second-level schools. Those surveyed had participated in seminars run by the company.
The latest figures underline the boom in the grind culture. The State's largest grind school - the Institute of Education in Dublin - is thought to generate over €9 million in student fees a year.
This year, about 800 students completed their Leaving Cert at the institute, where full-time students pay fees of about €5,000 a year. Once a Dublin phenomenon, grind schools are now being established in all the major provincial cities and towns.
A striking feature of the new survey is the high rating given by students to their teachers. There was considerable controversy earlier this year when the ratemyteachers.ie website - which allows students to rate teachers anonymously - published many negative comments about teachers.
However, over 70 per cent of students in the latest survey rated their teachers as "excellent". They said the most important skill of a teacher was an ability to impart subject knowledge effectively. They also thought an ideal teacher should be fair, motivating, humorous, caring and dedicated.
The survey found that Leaving Cert students spent an average of 18.5 hours per week studying and doing homework. The most hard-working students were in Cork, Limerick and Galway.
