He said unfilled vacancies should be taken into account when producing the school performance tables.
"This shows there is much more to school performance than structures, " said Mr Twigg.
The school performance tables are also being expanded to show a wider range of information.
The courses are likely to start in 2014 with the new qualifications included in school performance tables from 2016.
It offers rankings for health and life expectancy, employment, school performance and climate.
The main success so far has been to make school performance more transparent.
Ministers have said they will give it prominence in school performance league tables.
In the latest national assessment of school performance, 40% of American ten-year-olds were unable to read at their grade level.
We need to target the worst schools and establish excuse-free zones in education, beginning with real measures of school performance.
Brian Lightman, general secretary of the Association of School and College Leaders, cautioned against the over-simplified use of school performance data.
Back in February, Ms Gilbert urged teachers to write and complain to her about inspectors' over-zealous use of school performance data.
BBC: NEWS | UK | Education | Half of appeals to Ofsted upheld
But finally, so much of school performance also has to do with attitudes at home with parents and in the community.
Ministers had pointed to the relatively higher improvement in results in specialist schools when they published last year's school performance tables.
They have damaged public school performance and student prospects in a time of heated global competition for smart industries and educated workers.
In his letter, Mr Moore calls for the immediate suspension of school performance tables, saying a "snapshot of school achievement" was damaging.
Is this a company dominated by siege mentality, unable to recognize that deep value pricing is its last hope for a tolerable back-to-school performance?
It's also clear that there's much we want to know about student, teacher and school performance that cannot be determined from test results alone.
One last point which I always have to remind people of -- I said that the biggest ingredient in school performance is the teacher.
In what has become a polarised argument, other vital issues such as the quality of teaching or evaluations of school performance have hardly been broached.
It's clear that systems that gauge student, teacher and school performance on standardized test scores put intense pressure on those results and inevitably tempt people to finagle them.
If that could be done, the pressure to be able to terminate them would be significant, and that could do a lot to improve school performance right there.
With school performance measures, common core standards and value-added learning now being accepted into the community mainstream, perhaps new consumer choices for pupils, parents and taxpayers will expand.
Liberal Democrat AM Aled Roberts argued that by concentrating on overall school performance this banding system fails to acknowledge the individual performances of pupils and departments within those schools.
Under the plans, there will be changes to school performance tables, Ofsted inspections and governance, and a "pupil premium" system will channel more money to the most deprived children.
Greater political significance attaches to the tests for 11-year-olds in England, because they are published towards the end of the year and form the basis of the primary school performance tables.
They have driven our states and municipalities to the edge of bankruptcy and have damaged public school performance and student prospects in a time of heated global competition for smart industries and educated workers.
Has your child experienced any changes in school performance?
Launched in 1997, the tests are taken every three years by a sample of schools in over 70 countries and regional authorities and are used to create a global ranking of school performance.
The English Baccalaureate was introduced as a measure of school performance, appearing in league tables, and showing the proportion of pupils achieving GCSEs grade C and above and some AS-levels in specified key subjects.
The best-known measure is, of course, the Scholastic Aptitude Test, taken by college-bound seniors only but widely used as a proxy for school performance despite its proprietor's continuous protestations that it was not designed for that purpose.
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