One-in-three teachers says poor broadband connectivity is hampering online schooling for exams during the Covid-19 crisis.
A new survey from the Studyclix website also found more than 50% of teachers in some counties have bad internet connections.
The findings show teachers in Mayo, Cavan, Kilkenny, Mayo and Wexford have the highest rate of slow or bad internet coverage.
Founder of Studyclix, Luke Sanders, says many students also do not have the online access needed to help them prepare for the Leaving Cert.
"I think already this Leaving Cert of 2020 is probably going to be the most divided," he said.
"Some students are kind of proceeding with full access to the internet, full access to their teachers and others are really being left behind by both internet and access to laptops and iPads and so on."