Beccles Free School faced widespread opposition from political leaders and other school heads who believed that the town was the wrong place for such an establishment.
But students, staff and governors silenced their critics after receiving both good and outstanding results.
The school, run by the Seckford Foundation Free Schools Trust, opened in Carlton Colville, near Lowestoft, in September 2012, but will be moving to the Beccles Middle School site in Castle Hill this September. It currently has 198 pupils on roll from year seven to 10 and will include year 11 students from the autumn term.
Inspectors graded it as a good school for overall effectiveness, as well as the quality of teaching and leadership and management.
It received an outstanding grade for the behaviour and safety of pupils.
The report said: “Behaviour in the classroom is exemplary – inspectors saw no examples of students challenging a teacher or trying to distract each other, so that the vast majority of time in the classroom is actually spent engaged in learning.
John Lucas, headteacher, said: “We are all delighted with this report and it is a great credit to our students. We are very proud of their role in the success of the school and the way their behaviour has been noted as outstanding from Ofsted.”