More students have chosen to attempt higher level subjects in the Leaving Cert since the grading system was revised.
However, new research from the ESRI shows that performance levels among students taking higher level subjects have now dropped.
The way the Leaving Cert is graded was changed two years ago to try to relieve some of the pressure on students.
There are now eight different marks that can be awarded, where previously there was 14.
The changes have caused an increase in the number of students attempting higher level subjects. There has been a 2% and 4% increase in higher level Maths and Irish.
However, Research Professor with the ESRI Selina McCoy says there is a downside.
Ms McCoy said: "We found that more students were performing at a much lower level in higher level, so they weren't achieving the higher grades.
"We felt that this was not necessarily a positive outcome of the reform."
DEIS Schools did not record the same level of increases in higher-level take up.
This means the gap between DEIS and non-DEIS schools in terms of higher level students has widened.
Students in the study say they think there is now too big a difference between the points awarded for higher and ordinary level papers which does not reflect the effort and workload involved at ordinary level.