Schools are still facing intimidation in the wake of the Trojan Horse scandal, including dead animals in the playground and even death threats, it has been claimed.
Headteachers argued that the problems raised by the alleged plot had "not gone away" with some schools feeling pressure from outside over issues such as teaching against homophobia.
Four separate investigations were conducted into the alleged Trojan Horse plot by hardline Muslims to seize control of a number of school governing boards in Birmingham.
While no evidence of radicalisation was found, the findings did raise concerns that in some cases, governors had exerted inappropriate influence over how schools were run.
At the National Association of Head Teachers (NAHT) annual conference earlier today, delegates raised concerns that no school governor implicated in the scandal has been investigated or banned, and called for a database of individuals removed from governing bodies.
Sarah Hewitt-Clarkson, head of Anderton Park School in Birmingham, told the conference: "Trojan Horse has not gone away. Those of us who were involved, we knew it was the tip of the iceberg. We still have dead animals hung on the gates of schools, dismembered cats on playgrounds. We have petitions outside schools, objecting to teachers teaching against homophobia."
She said she had been sent a death threat on social media, in which someone had written "any headteacher who teaches my children it's alright to be gay will be at the end of my shotgun'."
Speaking after a debate on the issue, Ms Hewitt-Clarkson said she was not aware of other death threats, adding that she knew about one school which had found a dismembered cat in the playground, while another had a dog hanging from the railings.
She said she does not know why this is happening, suggesting it may be to intimidate people or could be an accident.
The union backed a resolution raising concerns that the recommendations of the Government-commissioned Clarke report into the Trojan Horse scandal have not been fully implemented.
NAHT member Alison Marshall told the conference: "Nine months after the Clarke report was published, with recommendations so clearly stated, very strong evidence given by our members and colleagues, we are still a long way from implementing those recommendations.
"Nicky Morgan stated in January that the Government had accepted every one of Peter Clarke's recommendations. We need to exert pressure to ensure that these recommendations are truly delivered, not in a superficial way and certainly not watered down."
Ms Marshall later added: "Despite all the evidence we have, we're faced with a situation where not one single governor implicated in the Trojan Horse scandal, has been investigated or even banned.
"Where is the justice in that?" Ms Hewitt-Clarkson told delegates: "All the behaviours and things we saw before are still there. So to have promises that have been broken, not followed through, are absolutely unhelpful, unsupportive and have left open gaps for certain individuals to start up again."
The union specifically raised concerns that recommendations in the Clarke report around limiting the number of governing bodies one person can sit on, and preventing certain individuals from being involved in running schools have not been acted on.
Delegate Tim Gallagher said that because governors are volunteers, there is limited legislation in the area.
He told the conference it is "blindingly obvious" that in a "loose, largely unregulated framework" inappropriate behaviour can be found in the governance of schools.
"It does not need to be as profoundly dangerous as that found in Birmingham, it can be the micro-managing of a school to the detriment of our members and the school itself," he said.
Mr Gallagher told the conference: "We need high quality, mandatory governor training. We need to regulate the number of governing body posts any one individual can hold. We need a database of governors and we need to be able to keep a check of the suitability of governors."
Education Secretary Nicky Morgan, who was not present for the debate, said: "There is no place for extremism in our schools and we continue, absolutely, to work to eliminate any form of extremism."
The Government has been working with local schools and Birmingham City council to ensure there is not a repeat of the scandal which hit the city's schools last year, she said.
Mrs Morgan added: "This is a reminder that this is a serious issue and something that is not going to be solved overnight. We have taken action to remove and continue to take action to remove people from being in schools who don't follow British values."
A lot of work has been done on implementing the Clarke recommendations, Mrs Morgan said, adding that the Conservative party has an extremism strategy in its election manifesto.
If the party is in power after the General Election, this would be worked on immediately by the Prime Minister, the Home Secretary and others, the Education Secretary said, adding that a database of governors would be a discussion for the next extremism taskforce.
It was not made clear at the conference who may be behind any intimidation of schools.