The secondary school teachers' union, the Post Primary Teachers Association, has launched its election campaign by calling for smaller class sizes.
The PPTA says it hopes a full-page newspaper advertisement published on 5 October will prompt all political parties to prioritise the reduction of high school class numbers.
It says teen pregnancy and crime are just two of the consequences of bigger classes.
PPTA president Robin Duff says class sizes are out of step with a new look education system.
Mr Duff says the newspaper advertisement abides by the Electoral Finance Act and there is no connection with recent advertising on smaller classes by the Labour Party.