Two Christchurch Girls' High School students say their Black Lives Matter posters were removed last week by a staff member - who then told them that "all lives matter".
Students from Auckland's Marist College and Christchurch's St Andrew's College also complained about staff removing posters promoting the movement.
The two Year 13 students at Christchurch Girls' High School put up their posters last week after attending a Black Lives Matter rally in the city on Queen's Birthday.
One girl, Angela*, said after removing the posters the member of staff claimed they were damaging walls.
"But there were other posters that were up with tape on the same surfaces and they have never been taken down before," she said.
The students then complained to senior management.
"So we went and we tried to talk to another senior member of staff and when we asked him about it, he just said it was in case the school surfaces got damaged and we were told not to get upset over posters and that we didn't need to argue," Angela said.
Another student, Audrey*, said staff were then ordered by senior management to not remove the posters - but they were never given a proper explanation why their posters were originally removed.
"They have told staff that the reason the posters were taken down was because of the tape and the Blu-tack damaging walls," she said.
"But they haven't been told that this member of staff said 'all lives matter' and that was actually the reason he took them down."
The incident at Christchurch Girls' High comes after similar complaints by students at St Andrew's College and Marist College.
Marist student Nia Cherrington said casual racism was an issue at her school.
"We've had a lot of issues with the teachers trying to portray their own views on our girls, saying things like 'but all lives matter', and also a lot of things about how Māori don't deserve scholarships," she said.
Need students engaged with world around them - PM
Prime Minister Jacinda Ardern said the matters were for schools to deal with, but she did not discourage the students' actions.
"Ultimately, as I say, that is a matter for schools to manage but I think we're all better off when we have young people who are engaged in the world around them, that are thinking critically about the world around them."
Massey University sociologist Professor Paul Spoonley said it was deeply disappointing that the posters were being torn down in some schools.
"So what's the school doing? Well, I think it's first of all censoring what the students want to do and say, but secondly, it appears to be institutional racism - racism that has come from the school itself," he said.
Spoonley said schools should be allowing their students think freely.
"What we really want to do is teach our students to be good citizens and part of that is being aware of social divisions and in this case, ethnic divisions," he said.
Social issues important - Ministry of Education
The Ministry of Education's deputy secretary for sector enablement and support, Katrina Casey, said awareness of social issues was an important aspect of growing and learning.
"We encourage students to participate as critical, informed and responsible citizens and schools may want to follow up their students' interest in social issues," she said.
"Schools are the best placed to make decisions about how they want to respond to student actions in consultation with their parent communities. If students or parents have any concerns, we encourage them to contact the school in the first instance."
The Teaching Council - the professional body for the teaching sector - said it was yet to receive any complaints or mandatory reports regarding the alleged incidents.
St Andrew's College rector Christine Leighton said the outburst by its teacher was now a disciplinary matter and its outcome would remain confidential.
"The teacher (Ngāi Tahu) has dedicated her life to equity and equal opportunity for Māori. She is concerned about racist attitudes within New Zealand society and is committed to addressing these. The college honours this commitment," she said.
Marist principal Raechelle Taulu said: "Marist College is aware of the concern our young people have about racism in our society and in the world. We stand with them in sharing the rejection of actions and attitudes that are racist and violent.
"We are working with our student leaders to help them share this message with our community, while also recognising that we are governed by policies and procedures. The school board and senior management take any claims of racism seriously and we are reviewing the issues raised with us.
"As always, the wellbeing of our students is our priority and this will be at the forefront of any decisions we make within the guidelines of our policies and Catholic education."
Christchurch Girls' High School said its principal was unavailable today.
* The two Christchurch Girls' students did not want their real names used in this article.