Forget your calculator, or chatter in class twice, and you get a warning.

Do it a third time, and you'll land in detention the same day.

The three strikes behaviour policy at the Warriner School, in Bloxham, was one of the changes introduced by headteacher Dr Annabel Kay, which has led to the school getting a glowing Ofsted report, after an inspection last month.

Dr Kay took over the school in April last year.

Under the new, stricter regime, the school was rated good by Ofsted in every category – and Dr Kay was praised for providing “transformational leadership”.

She said: “I am over the moon they have acknowledged how much we have achieved in the year, because there has been a lot of change in the school.

“We have had a real focus on what outstanding teaching looks like and spent a year unpicking with our teaching staff what it means to be an outstanding teacher.”

Dr Kay said that once the changes she had implemented were fully embedded, the school would be outstanding.

She said the new detention system was initially unpopular among students but it had been “hugely effective”.

She added: “In maths they were repeatedly arriving without calculators and delaying the lesson.

“Behaviour has improved hugely and it has also enabled us to identify repeat offenders, who have organisational issues, so we can work with them.

“In the past there was no support for them.”

In his report, Ofsted inspector Simon Rowe said: “The new headteacher has worked demonstrably to improve the quality of teaching, raise achievement and improve behaviour since her arrival.”

Prefect Thomas Dence, 14, said: “Since the new head’s come in, the school has made a really good improvement.”

Fellow prefect Charlotte Parsons, also 14, added: “The behaviour rules have had the biggest impact, because you don’t get as many students disrupting lessons and you get more work done.”