Beaumont School, Oakwood Drive, received the highest accolade across the board, including leadership, quality of teaching, achievement and behaviour of students, following a two-day inspection.
It converted to become an academy school in 2012.
Being judged as outstanding marks an improvement at Beaumont, which was rated “good” both after an inspection in 2008 and during an interim assessment two years ago.
Inspectors commented: “Students receive an outstanding education at Beaumont School that prepares them extremely well for the future. Teaching is consistently good and much of it outstanding.
“Students are very respectful towards each other and their teachers. The behaviour and attitudes of students is exemplary in and out of the classroom. Students are very proud of their school.”
Inspectors praised the sixth form as outstanding, saying that the majority of students went on to their first choice university.
They added: “Governors and senior leaders set themselves very high standards.
“The school is a calm and purposeful place in which to learn.”
Headteacher Elizabeth Hitch thanked staff, students, parents and governors for contributing to Beaumont’s success.
Chair of governors Alex Hall said inspectors had described the school as a “breath of fresh air” and that they had observed some of the best teaching practice in their inspecting careers.