More than 5,600 pupils were excluded from classrooms across Sheffield - with one school alone accountable for more than a quarter of the figure.
A Freedom of Information request showed that a total of 5,688 secondary school children were excluded for a set period of time between 2015 an 2016 before being allowed back into lessons.
Outwood Academy City, which had 942 pupils handed out 1,533 fixed exclusions during the 2015/16 academic year, representing 27 per cent of the entire number across Sheffield.
Martyn Oliver, chief executive of Outwood Grange Academy City, said the academy had 'transformed' since 2015/16.
He said: "This is a school which the community are proud of and rightly so. Historically exclusion rates were high but standards of behaviour, which allows students to learn in a calm environment, have improved so much that today they have dropped dramatically and are at an all-time low.
"Fixed exclusions are currently running 60 per cent lower than the 2015/16 figure and continue to fall rapidly every day as students have risen their aspirations to meet our standards.
"Walking around the academy and speaking to students I have met dozens of children this morning whose attitude to learning has been transformed and seen classrooms which are calm and purposeful."
Mr Oliver added that exclusions were used as part of a 'positive behaviour policy, where students are given many chances to rectify their behaviour'.
He added: "If a school has high exclusions and outcomes for children are low, you would quite rightly think that it was a school in chaos. However, where exclusions are used to raise standards and they are falling rapidly over time, as they are at Outwood Academy City, it is a sign that a school is transforming, not only student outcomes but attitudes and behaviours which will allow children to play a positive role in the community and prepares them well for life."
The figures, which equate to 18.75 per cent of the total number of secondary school pupils being banned from the classroom, prompted Ofsted to write to headteachers in February.
The 2015/16 rate was also more than 1,800 higher than in the 2014/15 academic year, when 3,875 pupils were handed fixed exclusions and 82 permanently excluded from school.
The city was ranked in the top ten for the number of fixed period exclusions received by secondary school students and Ofsted's regional director for the North East and Yorkshire and the Humber, Cathy Kirby wrote to schools to raise her concerns.
She also called on inspectors to look very carefully at schools’ use of exclusion when making judgements about leadership and management and pupils’ behaviour.
A fixed-period exclusion means a pupil is barred from attending school for a set period of time, which can be anything from part of a school day up to a maximum of 45 days within a single academic year. This does not have to be continuous; pupils can be excluded for more than one fixed period.
In addition to the fixed-term exclusion figure, 75 children were permanently excluded from secondary schools across the city - compared to 82 in 2014/15.
Sheffield Council also approved plans in September to bring in further measures to bring down the exclusion rate, including creating six 'engagement hubs' to help troubled pupils to reintegrate into mainstream schooling.