The ongoing teacher shortage is affecting almost every secondary school in the country, according to the ASTI teachers' trade union.
Publishing the findings of a survey in advance of its annual conference next week, it said three quarters of the second level school principals who participated said they had received no applications for an advertised teaching post or posts in the current school year.
The union said the survey findings showed unfilled teaching vacancies in almost half of all second-level schools.
Just over 2,000 of the union’s members responded to the online questionnaire sent to them by polling company Red C, including 56 school principals.
Four out of five of those school principals said that they had employed at least one unqualified teacher this school year.
The union says the survey showed almost one fifth of schools was forced to remove a subject or subjects from their curriculum as a result of the shortage of teachers.
It says other strategies used by schools to deal with teacher supply issues included delegating additional work to teachers in the school and reassigning special education needs teachers to mainstream classes.
It said recruitment problems were compounded by the non-availability of substitute teachers, with nine out of ten schools surveyed encountering situations where no substitute teachers were available to fill teacher absences due to sick leave and other short-term absences.
The survey of teachers and school leaders was undertaken last month.
Teachers who participated in the survey identified remuneration as a key factor in causing the teacher shortage.
More than 70% of principals told surveyors that teachers were emigrating to get better paid jobs abroad.
The survey found that 70% said the cost of the two-year postgraduate qualification required to qualify as a second-level teacher was a barrier, while 67% of teachers said that teaching was no longer viewed as an attractive profession.
Those surveyed also identified better remuneration in other careers and a legacy of unequal pay for teachers since 2010 as other factors.
They also said the housing crisis was causing teachers to emigrate.
ASTI President Miriam Duggan said the union was deeply concerned about the impact of teacher shortages on students.
"Today's survey reveals that schools are being forced to use unqualified teachers, to divert resources away from students with special education needs, and to drop subjects from the curriculum," she said.
"This is shocking. Teachers are being asked to teach subjects they are not qualified to teach, to supervise additional classes and to change their rotas at short notice.
"This invariably causes extra work and stress."
The survey also found that job satisfaction among teachers continues to drop.
Some 44% of teachers said they were satisfied or very satisfied with their job compared to 50% in 2022 and 63% in 2021.
More than three quarters said they have considered leaving the profession with over a quarter frequently considering doing so.
