Rush, the principal of decile-3 Hastings Intermediate, told Television NZ's Q&A programme on Sunday that he would be voting yes in the referendum.
"We don't want young people criminalised for their cannabis use. We think cannabis is a health issue, not a criminal issue," he said.
But today he said he had "over-reached" and had received "a bit of flak" from other principals for his comments.
"To be completely honest about it, that is my personal view. The position of the federation is that it's a conscience issue for principals," he said.
"That is something I just need to take responsibility for. I did over-reach myself. My comments were not an indication of the position of the NZPF [Principals' Federation]."
His comments were a surprise because most previous public statements by principals have opposed legalisation.
Patrick Walsh, of John Paul College in Rotorua, wrote in June that legalisation would be "a disaster for our young people".
The rector of of King's High School in Dunedin and the principal of St Joseph's School in Taranaki have been criticised after they made comments against legalisation in newsletters to parents, and St Paul's College in Ponsonby put up a billboard saying, "To legalise is to normalise - say no."
"There is this perception that cannabis isn't harmful, but it is, particularly to young brains," Walsh said.
"We know that it impacts memory, attention and the ability to problem-solve, and those effects can be permanent.
"There is also some evidence that it impairs judgment and concentration, and of course young people are not always the best for exercising judgment so anything that impairs their judgment can affect their safety."
Auckland Grammar School headmaster Tim O'Connor said he was "surprised that an organisation such as NZPF felt it appropriate to share a view on a pending referendum, that was allegedly on behalf of all principals".
"Its presentation was misleading. The cannabis legalisation and control referendum and the End of Life Choice referendum are matters for each voting age member of communities to make a decision on," he said.
Elim Christian College principal Murray Burton said most schools in the Principals' Federation are primary and intermediate schools, but he believed secondary principals "would be fairly actively dismayed" if the drug became legal.
"We take a fairly hard line on vaping, as we used to do with smoking in school uniform," he said.
"Although we could draw the boundaries very carefully, I think a change like that [legalisation] would mean it would be all over the school, it would mean untold distraction. Do we really need to have that?"
"We were guaranteed at the time by the Government that there would be very strict regulation to ensure that alcohol didn't get into the hands of people under 18," he said. "I just don't have a lot of faith in that."
But Nelson College headmaster Richard Dykes, who led a fight against vaping at his previous school Glendowie College, said he was actually undecided about the referendum after talking to principals in Canada, where cannabis was legalised in 2018.
"We put that question to principals there: have you noticed any change? They said no, they haven't," he said.
"They said the students for whom it was already a problem, it was still a problem. For those for whom it was not, it remains not a problem."
And surprisingly, Rush has some support for legalisation. Former federation principal Whetu Cormick said he was among the 73 per cent of Māori who took part in TVNZ's Vote Compass tool who supported legalisation - compared with 50 per cent support from all those who have used the tool.
"Why are Māori supporting it? Because they are the ones that end up in jail," he said.
He cited Drug Foundation data showing that 51 per cent of prisoners have been kicked out of their schools, and that 55 per cent of students kicked out because of drugs were Māori.
"It's wrong, of course, because it's illegal, but many of those kids come from families where this is just the norm," he said.
"At the moment, because it's illegal, we don't have a systematic approach to educating and allowing children to have that rich conversation about the pros and cons."
But Haley Milne of Kia Aroha College in Ōtara said she supported "decriminalising" cannabis, so that people were not jailed for possessing it, but she did not support "legalising" it.
Other principals, including Secondary Principals' Association president Deidre Shea, declined to comment on the issue because it was "a personal matter".
