Fifteen-year-olds would no longer be able to quit school early, under a bill tabled in Parliament yesterday.
A Ministry of Education crackdown on the exemptions already saw the number of students who got official permission not to go to school more than halve between 2006 and last year, when 1930 15-year-olds got approval.
But principals said while leaving school was a last resort, it had been the best answer for "special cases" not suited to being kept in class.
"It's not as if schools have just willy-nilly said `bang, you've got to 15 and a half, you can go and get an exemption, goodbye'," said Secondary Principals Association president Peter Gall.
At times, students kept in school under the crackdown were on the roll but did not turn up.
Mr Gall said schools would need more resources and support to assist the students if the change went ahead.
"We can change the rules all day but that's not going to change the impact of the things that are happening in those young people's lives."
Education Minister Chris Carter said mechanisms were in place to pick up if students were not turning up and promised more were on the way.
He said the Government wanted to keep New Zealanders in formal education or training until 18 years old under a plan known as Schools Plus.
Removing early-leaving exemptions was a step in the wider plan and further details were due to be made public by the Prime Minister Helen Clark within the next month.
"The problem is that these kids are somewhere and if they're not at school, if they're not in alternative education and they're not in some sort of supported environment, they are on the streets _ and that's the last thing we want," said Mr Carter.
Last year, the rate of boys getting early leaving exemptions was twice that of girls.
Of all 15-year-olds to get permission to leave school last year, 76 per cent went to a training provider course, 18 per cent went into full-time employment and the rest went to a polytechnic, university or elsewhere.
The Education Amendment Bill proposed police vetting of all people with unsupervised access to children while schools and preschools were open.
It outlined an information matching programme to identify teachers in class without a practising certificate or authorisation. The bill offered measures to clarify roles of boards of trustees and increase the flexibility of when board elections were held. It included amendments to deter people from committing offences relating to student loans and allowances.