Secondary teachers say a government scheme is encouraging the wrong teenagers to leave school early and will harm school courses in subjects such as metalwork, cooking and sewing.
Delegates at the Post Primary Teachers Association conference in Wellington on Wednesday say the Government needs to take a closer look at its Youth Guarantee policy.
The scheme pays for 16- and 17-year-olds to study for free at tertiary institutions and is aimed at those who are at risk of dropping out of education.
But the PPTA says some institutions are enrolling teenagers who could, and should, stay at school.
The union also says some organisations are trying to enrol students before they have finished Year 11 at school.
It is worried an increase in the number of teenagers covered by the policy will leave some schools with too few students in their technology classes.
PPTA's Southland representative Penney Dunckley says a looming increase in Youth Guarantee places could hurt technology classes, especially in small schools.