Almost 40% of teachers in Donegal are currently experiencing slow or bad internet coverage.
According to Studyclix.ie's survey, teachers in the county also said that two in five pupils don't have access to a device or internet for schoolwork.
78 per cent of teachers nationwide believe a lack of student engagement is a barrier to online schooling during the coronavirus crisis.
The worst affected areas are Kilkenny, Cavan, Mayo and Wexford, while larger urban areas report better connectivity.
Luke Sanders, from Studyclix.ie, says broadband coverage is causing serious problems ahead of the Leaving Cert: