Overton Grange School in Sutton has been graded “good with outstanding features” after Ofsted inspectors turned up without warning.
The education watchdog has been trialling no-notice inspections to prevent teachers rehearsing and giving skewed impressions.
Ofsted inspector Alan Taylor-Bennett said: “The quality of learning is good because of students’ positive attitudes and the interest and willingness to learn, which they show in response to the good teaching.
"Students’ behaviour is good and the school is a safe and happy environment; staff know the students very well and take their well-being and achievement very seriously."
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