Pupils were sent home today after an incident broke out on school grounds.
The Oxford Academy was forced to close earlier today with staff and pupils leaving hours ahead of the bell ringing.
An open evening that was scheduled for later today has also been cancelled as a result.
A spokesman for the school said "a small group of boys" had "decided to push back" against recent changes introduced for behaviour regulations.
Katie Heeley, whose best friend's niece attends the school, said: "My friend was quite panicked and she was very upset and sad by what had happened.
"She lives about two minutes away and literally ran to the school when she found out.
"It's very bad. Her niece was crying and very scared. A lot of people were saying they will not be sending their kids back there again.
"The school had to be shut and students sent home. They were meant to be having an open event this evening but have had to cancel due to how unsafe it is."
She believes the kids were asked to leave the school between the hours of 10am and 11am.
It is understood that no weapons were used during the incident despite speculation on social media.
A spokesman for the school, which is part of the River Learning Trust, said: “Over the last few years we have significantly improved behaviour and are creating an environment in which students behave well, are happy and are able to flourish.
“This process is ongoing, and to allow the school to continue its journey of improvement, there have been further recent changes relating to behaviour and high expectations of students.
“These changes have been welcomed by the majority of students, families and staff.
“A small section of the student body has decided that it wants to push back against the changes.
“This led to students displaying behaviour today similar to that seen on social media in other UK schools earlier in the year, when some students joined in staged, artificial and disruptive events.
“There certainly is not significant opposition among students to The Oxford Academy being a school that aims to serve its community and give its young people great life chances.
“We don’t apologise for having high expectations of our students. We know this is the right thing to do.”
A Thames Valley Police spokesman added that the matter is not being treated as a police incident.
The Oxford Academy is located in Sandy Lane West in Littlemore.