The cost of substitute teachers in Northern Ireland has increased to more than £66 million, the Audit Office has said.
Expense from covering permanent staff absence is up 40% since 2000, the public spending watchdog added. Stand-ins are paid up to £139 a day.
Covering vacancies and increased amounts of maternity leave contributed to the cost, the audit report said. Temporary teaching can affect pupil learning and achievement, it warned.
The dossier said: "While substitute teachers are needed to maintain the smooth running of schools, costs have risen dramatically."
Expenditure on substitute teaching has increased in real terms from equivalent to £47 million in 2000/01 to £66.07 million in 2008/09.
There was significant inflation in the cost of covering vacant posts. The auditor said this might reflect an increase in vacancies of a temporary nature or a tendency by schools to recruit on a temporary basis. However, the category of vacant posts is also used by the Department for Education to an unknown extent as a default when schools fail to provide it with a reason for the absence of a permanent teacher so will be overstated.
There has been a rise in the number taking maternity leave as well as in the average length of time allowed. There is also extended leave of absence for paternity or adoption.
Prematurely retired educators were still responsible for a significant proportion of casual work leaving new graduates struggling to find work.
The Department of Education has introduced legislation making employers liable for the full cost of teachers' premature retirement, anticipating this will limit the practice and over time reduce the number of prematurely retired teachers available to provide substitute cover. They provided 62,310 days of help in 2008/09, 13% of the total which is the same as in 2000/01. This is equal to around 320 permanent teachers.
Northern Ireland Audit Office (Northern Ireland Audit Office )