A secondary school in Carlisle where police were called to a protest by parents and students outside the school gates after missiles were thrown has insisted staff are working “tirelessly” to improve children’s lives.

A peaceful demonstration by parents over behaviour policies at Richard Rose Central Academy (RRCA) on Wednesday afternoon quickly became heated and plastic bottles and stones were thrown, leading to pupils and teachers being kept inside school buildings.

Dozens of parents and students joined the protest outside the school in the centre of Carlisle, with one waving a sign reading “HMP RRCA”. They presented the school with a list of complaints over the school’s uniform and discipline policies and the separation of different year groups at break times.

A spokesperson for the school, which is part of the United Learning multi-academy trust, said its policies were supported by “the overwhelming majority of parents and students” and were responsible for the school’s improved results and positive reports from Ofsted inspectors.

“The well-publicised parent protest attracted fewer than 20 parents. The events that sadly took place after their protest by a number of pupils, egged on by some parents, have been condemned widely across the parental and local community,” the spokesperson said.

“Staff at Richard Rose Central work tirelessly to improve the lives of the children they teach and everyone is disappointed that the actions of some students, encouraged by a small group of adults, has drawn this attention to the school, which has been doing so well.”

On Thursday there was a police presence outside the school gates and no repeat of the protests. Several parents collecting their children said they supported the school’s policies.

“I understand why they’re doing it. You tell the kids what to wear but they push it to the limit or they go too far,” said Daniel Scotney, who has a child in year seven. He said the protest was “threatening” for students and staff. “It’s got out of hand. It’s out of order. People shouldn’t have to be worried about being hit by someone throwing something.”

He added: “I think one-to-one conversations are the only way to get things solved. It’s intimidating having 100-plus people outside there. It isn’t all down to the school, it’s down to the kids and parents as well.”

Several of the parents involved said they were protesting over school sanctions, including what the academy calls “internal exclusion” for behaviour breaches. Another issue has been changes at lunchtimes: due to safety concerns over the large number of students gathering in the school’s atrium, zones restricted to individual year groups have been implemented.

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Nicola Clulow, 53, who has a son in year nine and who wrote an open letter to the principal and governors last week about the school’s policies and management, said: “This stupid protest has ruined the prospect of those of us parents with legitimate concerns from being heard or taken seriously. It’s very annoying.”

She claimed there was not enough time for some children to get food at lunchtimes because of long queues. “Some of these changes may sound trivial but there is a much bigger underlying issue around this regarding problems with discussion and communication and lack of understanding of the changes,” she said.

“This is not only by the students but staff too, resulting in inconsistent approaches and [pupils] being removed from classes for trivial reasons and worrying if they put a foot wrong – quite literally.”

Clulow said she could find only one message explaining changes of policy to parents on the academy’s website. “The parents I have asked were as unaware of it as I was. This is what we mean about communication issues. It’s not all about silly haircuts.”

One mother collecting her child after school said she could “totally understand” why changes had apparently been made. “The behaviour of some of the students is appalling. They believe they can do anything they want without having to face any consequences – and some parents encourage this behaviour,” she said.

“The school is just trying to teach them how to become respectful and responsible individuals. Unfortunately, although the majority of students don’t behave in this way, they are the ones having to put up with a set of very strict rules, because of these individuals.”

The mother said she believed the protest had backfired and some parents and pupils had been unwittingly caught up in the demonstration. “Many children were terrified, some parents couldn’t find their children, some kids couldn’t get to their buses. It was total chaos,” she said.

A student at the school, who asked not to be identified, said there was “not enough recognition for good things, only bad,” and the school’s use of “internal segregation” was putting pupils into isolation. “Education should take priority over a school’s reputation. People are scared to come to school because they’re scared of the new rules,” she claimed.

Michaela Rowley, 29, said her 14-year-old daughter had been excluded this week for arranging to include year 10 pupils in the protest. “She just wanted their voices to be heard,” said Rowley, adding that her daughter had previously been excluded for wearing “the wrong pants”.

Amanda Skelton said she wanted to take legal action over the school’s use of internal segregation. “My son was kicked out on his first day back at school after just eight minutes because they said his hair was too short. They put him in isolation and said he’d be in there till his hair grows back,” she said.

The spokesman for United Learning told the Guardian: “There haven’t been rule changes. The school has had the same rules on behaviour, uniform and expectation in place for a number of years. Over the past few years these higher expectations have been part of the initiatives we have put in place which has significantly improved education at the school, resulting in its first ever grading of ‘good’ by Ofsted.

“Internal exclusion is not a new rule and has been in place in the school for some time. It involves students having access to a full curriculum but away from their usual class.”