The long-awaited national data system showing schools how well they are performing was published this week. A set of "benchmarks" has been sent to every primary and secondary school.
The benchmarks, a series of statistical tables, allow heads and governors to compare their results in national curriculum tests and GCSE exams against the national averages for schools in similar social and economic circumstances.
From next September, they will be obliged to set their own school targets for academic improvement, using this week's publication as a guide.
The Government's curriculum quango, the Qualifications and Curriculum Authority, said the new statistical tables would "puncture complacency" across the system.
"For too long schools have been in the dark about how others like them are performing nationally," said David Hawker, head of the QCA's curriculum and assessment division.
"This has often meant that underachievement is not properly recognised and tackled. Now for the first time this information is available in easy-to-read tables. They will throw into sharp relief the disparity between schools in similar circumstances," he said.
The tables are grouped according to factors such as the number of pupils taking free school meals, and the proportion speaking English as an additional language.
At key stage 2, for example, a head would be able to examine the national averages for the category of schools where more than 50 per cent of pupils speak English as a first language, but where between 36 and 50 per cent are eligible for free school meals.
The benchmark tables show the cut-off points for the bottom 25 per cent of pupils ranked by achievement, the top 25 per cent, the top 5 per cent and the median.
Schools will be receiving a further set of comparative information through a separate data initiative from the Office for Standards in Education.
OFSTED's Performance and Assessment data (PANDA) will perform a similar function. Incorporating parts of this week's benchmarking data, it will provide comparisons be-tween similar schools, too.
Both organisations are keen to address the wide variations in performance among schools in the same area.
Even the most favoured schools, where fewer than 9 per cent of pupils take free school meals, vary greatly. In those schools forming the top 25 per cent, 87 per cent or more of 11-year-olds reach the expected standard (Level 4) in literacy. Yet the bottom 25 per cent achieve only 68 per cent or worse.
The same scale of variation can be seen in the more typical category where between 9 and 20 per cent receive free meals. Here the top 25 per cent of schools get 78 per cent or more of their pupils up to Level 4. The bottom 25 per cent achieve 59 per cent or less.
Despite this range of scores, the effect of poverty is also clear from the list of median scores (the middle point in the achievement range). The median score for socially privileged schools is 78 per cent. This falls steadily down to 41 per cent among those schools where more than half the children are eligible for free school meals.
None the less, as ministers like to point out, even in this category there are some schools (5 per cent) where at least 68 per cent of their 11-year-olds reach the expected standard.