It is the differences in performance within schools, rather than those between them, that are key to raising education standards, according to many respected international research projects.
But last week a school leader in England accused officials of "writing- off" a project specifically designed to address the problem of "in-school variation".
Richard Fitzgerald is deputy head at All Saints Catholic School in Dagenham - one of a group of 20 secondaries that trialled different ways of tackling the issue in a project run by the Training and Development Agency for Schools (TDA) and the National College for School Leadership.
The school found that using the expertise of one of its departments to improve standards in another led to tangible improvements.
But Mr Fitzgerald says the removal of funding has meant the end of plans for the pilot schools to spread the techniques trialled through the research to clusters of other schools.
"They are missing out on a useful and proven method of school improvement. It is about the lack of money and it is also about the drive. If there is drive coming from above saying, `We want you to work with other schools', then it will happen. But take that drive away and it won't. There isn't impetus behind this project any more. It has effectively been written off and cut dead."
The UK education system has one of the highest levels of variation in pupil outcomes of the world's industrialised economies, according to the Organisation for Economic Co-operation and Development (OECD).
Mr Fitzgerald said the trials his school took part in looked at ways of tackling in-school variation. They included using data, standardising procedures across departments, looking at teaching and learning, and leadership and management.
But the school found the use of "student voice" - gathering pupils' opinions on their lessons - to be the most effective.
The school also paired different departments together and saw a "considerable" improvement in technology results after teachers worked with their counterparts in art. A similar approach in science saw A-level physics and chemistry results brought up to the level seen in biology.
All Saints has now also used pupil voice to help change its homework and exam-preparation systems.
The TDA confirmed that funding for the project ceased last year, but said 100 schools a month were viewing the resources it had produced. However, those like Mr Fitzgerald, who have seen the power of tackling in-school variation, believe it will need more than a website to realise its full potential.
Question time Using student voice to reduce in-school variation - questions to consider: Source: Reducing In-school Variation, a report by the Training and Development Agency for Schools and the National College for School Leadership.
Using student voice to reduce in-school variation - questions to consider: Source: Reducing In-school Variation, a report by the Training and Development Agency for Schools and the National College for School Leadership.
Source: Reducing In-school Variation, a report by the Training and Development Agency for Schools and the National College for School Leadership.