Guide: Secondary league tables

Every year the government provides data on attainment, progress and absence in all of England's secondary schools.

Media organisations, including the BBC, then use the information to compile so-called league tables. This guide explains the measures used, and how the information is displayed in our tables.

GCSE AND EQUIVALENTS

The key government benchmark for the attainment of Key Stage 4 pupils (aged 15-16), is the percentage of pupils gaining the equivalent of at least five A*-C GCSE passes, including English and maths.

The Labour government set a target that no schools should have fewer than 30% of students reaching this standard by 2011. The Conservative-Lib Dem coalition has, however, raised the "floor target" to 35%, although schools with low attainment where students are still progressing fast enough will not be considered underperforming.

In the tables, vocational qualifications such as BTecs and NVQs are given equivalency scores to GCSEs - some qualifications can count for up to four GCSEs.

From this year, some International GCSEs - but only those accredited by Ofqual - will also be included in the tables. These are taught in many independent schools, and their exclusion has in the past put many high-performing schools at the bottom of the tables.

The fact that some exam boards' iGCSEs are still excluded this year has meant low scores again for some top schools.

GCSE AVERAGE POINT SCORE

Each GCSE-level qualification and grade is given a specific score in points, enabling an average point score per pupil to be calculated for each school. This is used as a tie-break in the BBC tables, when they are sorted by the GCSE benchmark, although the average point score figures themselves are not included.

The points scores can be seen on the government data page for each school, reached by clicking on the school's name in the table.

ENGLISH BACCALAUREATE

This new measure, introduced in 2010, is the proportion of pupils in the school achieving A*-C passes in English, maths, two science subjects, a modern or ancient language and history or geography.

The government plans to award a certificate to pupils achieving this combination, but it is not currently a qualification in its own right. The government says its aim is to create an incentive for schools to offer these subjects, in order to give students "a properly rounded academic education".

Qualifications that will count towards the English baccalaureate are listed here.

In the BBC's tables, schools can be ranked by their English baccalaureate score, with GCSE points scores used as a tie-break.

CONTEXTUAL VALUE-ADDED (KS4)

This is a measure developed to show how much progress a school's pupils have made, in comparison with others from similar backgrounds in terms of factors such as deprivation, ethnicity and first language.

A CVA score is worked out for each pupil by comparing their achievement at Key Stage 4 (age 15-16) with that of other pupils from similar backgrounds nationally, who had similar prior attainment in their Sats - the national curriculum tests taken at Key Stage 2 (age 11).

Averaging these individual scores gives a score for the whole school. A formula is then used to convert this to a number based around 1,000.

Scores above 1,000 represent schools where pupils on average made more progress than similar pupils nationally, while scores below 1,000 represent schools where pupils made less progress.

Schools can be ranked in the BBC tables by their CVA scores, but this gives only a broad indication and the rankings should be treated with care. Each score has a "confidence interval" - a range of uncertainty. There is wider uncertainty around smaller schools' scores than larger ones, which means that comparing the scores is not exactly comparing like-with-like.

For various reasons, complete "before and after" scores are not available for all pupils. Where the data is missing for 50% or more of those eligible to take the tests, the CVA score is not published.

CVA scores are not published for independent schools, as the government does not collect the relevant data from them.

No national or local averages are given for CVA scores.

The government's detailed explanation of how CVA is calculated is here.

PROGRESS MEASURES

These were introduced in 2009, and show the proportion of pupils in a school making the progress expected of them between leaving primary school and finishing Key Stage 4 (age 15-16). Scores are given for both English and maths.

Pupils attaining Level 4 in their Sats are expected to get at least a C at GCSE; those with a Level 3 are expected to get at least a D, while those with a Level 5 are expected to get at least a B.

These measures are not published for independent schools, as their pupils are not required to do Sats so there is no data for comparison.

From 2010, the progress measure will be part of the floor target used to identify "underperforming" schools. Schools with fewer than 35% of students getting five A*-C GCSE passes including English and maths, which also score below the national median for both maths and English progress measures, will be considered underperforming.

In the BBC's league tables, English and maths progress measures are shown only in the table showing regional variations in attainment in England. But the data can be seen on the government's data page for each school, reached by clicking on the school's name.

If there is not enough data on a pupil - for example, if they have moved schools or recently arrived in the country - it may not be possible for them to be included in the calculation.

The proportion of pupils in any given school included in this calculation is given on the page for that school published by the government.

A/AS POINTS SCORE (PER PUPIL)

Students' attainment at Key Stage 5 - between the ages of 16 and 18 - is shown in the BBC's tables by the average number of points per pupil in a range of advanced level qualifications including A-level, AS level, the International Baccalaureate and some vocational qualifications.

A points system takes into account both the grade achieved and the volume of content covered in the course.

For example, an A* grade in a chemistry GCSE is 58 points; a merit award in a BTec First Diploma in applied science is 184. An average is then calculated per student for each school. The more qualifications undertaken by a student and the higher the grades achieved, the higher the average point score per student.

In the BBC's tables, the number of pupils at the school is used as a tie-break when the tables are ranked by A/AS-level point scores.

SECONDARY: A/AS POINTS SCORE (PER ENTRY)

Points are allocated for a range of advanced level qualifications including A-level, AS-level, the International Baccalaureate and some vocational qualifications, depending on the grade achieved. The number of points per entry is the total number of points achieved by pupils in a school, divided by the total number of exam entries.

It shows the average grade (higher scores mean better grades) per qualification for each school - whereas the points score per pupil reflects both the number of qualifications and the grades achieved.

This measure is only used in the BBC tables in the list of top-performing institutions at Key Stage 5, but can be seen on the government's data page for each individual institution.

KS5 VALUE-ADDED

This is a measure of pupils' progress between the end of Key Stage 4 (age 16) and Key Stage 5 (18). It is calculated in a similar way to "contextual value-added" (CVA) for KS4, but takes into account only gender, qualification type and size of the learning programme in question - not deprivation, ethnicity and first language.

Higher numbers indicate better progress. According to the Department for Education, in 2009, an institutional VA score of 1,030 meant that on average each of the school/college students achieved the equivalent of one A-level grade higher in one subject than the average attained by similar students. Conversely, a score of 970 meant that the school/college students achieved one grade lower than the average attained by similar students.

Schools and colleges can be ranked in the BBC tables by their CVA scores, but this gives only a broad indication and the rankings should be treated with care. Each score has a "confidence interval" - a range of uncertainty. There is wider uncertainty around smaller schools' scores than larger ones, which means that comparing the scores is not exactly comparing like-with-like.

For various reasons, complete "before and after" scores are not available for all pupils. Where the data is missing for 50% or more of those eligible to take the tests, the CVA score is not published.

Value-added scores are used in the BBC tables only in the list of top-performing institutions at A/AS-level, but can be seen on the government's data page for each individual institution.

INSTITUTION TYPES

In the name field of the BBC's league tables, schools may be marked as:

• IND (independent/fee-paying)

• SEL (schools which select on the basis of academic ability)

• AC (schools with academy status, which frees them from local authority control and carries certain financial benefits)

• SHUT (schools which closed during the academic year)

The government's data page for each school provides further information on whether it is a girls, boys or mixed school, its funding and governance arrangements and any subject specialism. Schools with some subject specialisms can select up to 10% of their pupils on the basis of aptitude for the specialism.

The tables include schools without sixth forms, schools with sixth forms, and further education colleges which take only 16-18 students. If a school has no pupils at Key Stage 4 (14-16), it will appear only when the tables are sorted by A-level points score; if it has no pupils at Key Stage 5 (16-18), it will appear only when the list is sorted by KS4 measures.

Sixth-form consortiums are listed as institutions, with average figures given for all their pupils. Results are also given for the pupils at the feeder schools for the consortium. The government's data page for each sixth form consortium lists its feeder schools.

Pupil referral units, hospital schools and unclassified test/exam centres are not included.

SCHOOL SIZE

The government does not publish data for schools with fewer than 10 pupils. These appear in the BBC tables, but SS is displayed in the data fields, and they disappear from the lists when the tables are sorted.

Data is displayed for schools with fewer than 30 pupils in the relevant year in the BBC tables, but these also disappear from the list when the tables are sorted and in our overall ranking lists showing top performers.

N/A - NOT AVAILABLE

If N/A appears in the results column, this can mean:

• The school has no pupils in the relevant age group - this may be because it does not have a sixth form, or is a further education college with no pupils aged under 16, or because it has opened recently

• The school has pupils in the Key Stage 4 age group, but did not enter any of them in relevant exams

• It will appear for independent schools in the CVA and progress measure columns, as these measures are not published for independent schools

• Results were not published for the year in question.