Two years ago Thomas Sumpter school was in serious decline. GCSE results had fallen for six years in succession, staff turnover was at 50 per cent and the school was at risk of being placed in special measures.
Today the school is improving thanks to an intensive programme of targeted support for its middle managers devised by new head Angela Briggs.
One spin-off of this programme has been its effect on within-school variation - the unexplained dips in students' results in different subjects and with different teachers.
When Mrs Briggs arrived at the secondary school in Scunthorpe, North Lincolnshire, there was a huge difference in examination performance between different subjects.
One department was an average of two GCSE grades below the rest of the school. Just 2 per cent of the department's GCSE students had gained at least five A* to Cs in the year before the intervention programme began.
Now dips like that are being ironed out - last summer that department saw a 19 percentage point jump in its results to 21 per cent. This increase is part of a bigger picture of improvement at Thomas Sumpter. GCSE results, although still poor, are on the way up.
Quality of teaching has also improved, and there is stability among the staff.
"We still have a long way to go, but the reputation of the school, from being absolutely rock bottom, is improving - no doubt about it," says Mrs Briggs.
Success in reducing within-school variation at schools like Thomas Sumpter has persuaded the National College for School Leadership to expand a project to tackle the issue.
According to international comparisons, variation is greater in British schools than in almost any other developed nation. Tackling the issue has become something of an educational Holy Grail.
For the past 18 months, 25 primary, secondary and special schools have been in pursuit of this Grail, through the NCSL's Leadership Network. From April this will be expanded to 50 when each school will partner another.
The project has identified areas that need to be addressed before a school can begin tackling the challenge. These include systematic and consistent use of data to inform practice, high-quality teaching through continuous professional development, and high-quality middle leaders.
Thomas Sumpter is an 11-16 comprehensive with 763 students. It serves a mixed catchment area, covering affluent areas as well as the poorest housing estate in North Lincolnshire.
In an inspection in May last year, Ofsted said that although there is still a lot of underachievement, excellent leadership has given the school new confidence and clear, commonly-shared purpose.
Angela Briggs must be one of the few secondary heads who have made the leap from running a primary school.
Until her arrival, the school had had intensive support from the education authority, but it seemed to no avail. "The consultants had worked directly alongside class teachers," she says. "The work had some impact at the time, but the minute they went it deteriorated."
Her response was to devise her own eight-week professional development programme where LEA consultants would come in and work intensively with heads of department, so they could then coach and mentor teachers within that department. Once those middle managers were skilled and confident, enough the gurus would leave them to get on with the job.
Mrs Briggs eased the administration burden and did a no-cover deal with heads of department, on the proviso that they spend that time mentoring people in their departments.
"What was absolutely important from the start was that I as headteacher took ownership of this project and drove it onwards," she says.
Another key issue was building trust. Over the years a degree of suspicion had built up between the school and the LEA.
"We didn't want people to feel this was being done to them. It was about winning hearts and minds, and the consultants establishing that trust was absolutely key."
The school had good data but it wasn't being used well. The programme started with a teaching and learning audit across each department, with consultants working with heads of department to analyse subject data.
Consultants then observed heads of department teaching and then feeding back to them.
But this wasn't a lesson observation - it was a lesson for the department heads on how to give teachers constructive feedback.
The next step involved planning, coaching and debriefing sessions with the teacher, head of department and the consultant.
Department heads would observe lessons while the consultant coached the teacher, and then swap roles to allow heads of department to coach.
"Since the consultants left our own heads of department have taken on this coaching and mentoring and they're now working across departments," says Mrs Briggs. "It has become self-sustaining."
Different schools involved in the NCSL's within-school variation project are finding different solutions to the problem. At St Vincent's RC primary in Warrington data are being used to feed into a colour-coded pupil tracker system which translates pupil levels into point scores.
Any pupils falling behind are immediately highlighted and targeted on by quality-improvement teams which aim to encourage consistent practice across the school by measures such as lesson observations.
Another secondary school found the appointment of "achievement co-ordinators" attached to each year group helped improve standards by up to 10 per cent.