One of a record 10 primaries in Lambeth, south London, to have been placed on special measures, it is now seen as a model for how an inner city school can transform itself.
It earned praise from Chris Woodhead, the chief inspector of schools, in his last annual report for the "very substantial" improvement in coming off special measures.
Yet just three years ago education was poor, with underachievement especially in English, maths and technology at key stages 1 and 2. Teaching at the voluntary aided school was unsatisfactory and there was serious disruption in class from aggressive and "dangerous" behaviour by some pupils.
Chris Cosgrave, 44, who joined as head teacher from a Surrey junior school six months after inspection, admitted: "Behaviour was a real problem. I had never seen anything like it.
"The noise in some classes was terrible and as a result work was very poor. The playground was a very unpleasant place because of the violence of some pupils."
Around 80 per cent of its 226 pupils are from ethnic minorities and for 50 per cent English is a second language; more than 70 per cent are entitled to free school meals.
Chris Cosgrave believes the school's fight-back was greatly assisted by a local education authority adviser, coupled with guidance from a diocesan official. They gave positive feedback and purpose to the staff, ensuring no one was blamed for the school's failure.
Chris Cosgrave and his deputy, Eileen Muresan - previously acting head - set about improving teaching through "modelling" of good practice, showing staff how children responded to good lessons and management.
Raising teacher expectations of more able children - neglected under the previous regime - was one aim. So, too, was a strong focus on literacy. The curriculum was better detailed in two-year, rather than previous one-year, chunks. And governors' roles were strengthened.
"Very quickly the feel of the place began to change and so did the quality of the children's work," said Chris Cosgrave.
In consultation with pupils, a behaviour code covering politeness and working quietly was established. Around Pounds 25,000, part of a legacy of underspending at St John, went on decorating and carpeting the warren of corridors and high-ceilinged classrooms, and landscaping the playground.
Mr Cosgrave said: "We wanted to give the children a different experience here to the one they get outside. Changing the school environment reinforces the expectation of quality."
In June last year inspectors found achievement was in line with national standards, with higher than average levels in writing. In mathematics many pupils achieved well. St John had a "purposeful work ethos" and "very effective" leadership, they said.