Mr Mick Shanley is the principal of a 320-pupil primary school in Corduff, a working-class estate in Blanchardstown in west Dublin.
He has experienced a growing problem in finding qualified substitute teachers since the beginning of the current school year.
In the past week he has had two teachers on sick leave. The first was replaced after two days by a substitute with no teaching qualification. The second has been out since Monday morning.
Yesterday afternoon Mr Shanley said he had "no guarantee" that a substitute would be found before that teacher returns next week, meaning that his class may be without a teacher for up to eight days.
A third teacher, who is out until June on maternity leave, has been replaced by a long-term substitute who again has no teaching qualification.
"The substitutes, all of them graduates, have turned out to be excellent, and all of them plan to follow a teaching career," said Mr Shanley yesterday. "But it indicates what a shortage there is. I can't fill those posts with qualified people. They're just not there."