Primary School League Tables

Okay, I get that I'm not supposed to undertstand these and that they're basically there so the Government can employ people to spew out meaningless data that attempts to make people think they're acually doing something but, and this is a big but, what the hell does the following explanation of the numbers actually mean?

Quoted from the BBC website:

Guide to the primary school tables

The tables show the published results achieved by schools in the Key Stage 2 national curriculum tests in England in May 2008.

Those are the tests pupils are required to sit in the final year of primary school, at the age of 10 or 11.

The tables use the results published by the Department for Children, Schools and Families.

They include "contextual value added" scores - produced by the department to show how much a school has improved its pupils' achievements since they took their first set of assessments in 2005.

The figures relate to all local authority-maintained primary and middle schools with pupils eligible for assessment at the time of the tests in English, maths and science in May.

They do not include special schools, pupil referral units, hospital schools or independent schools.

What is in the rankings

The schools are listed within each local authority (LA) in three ways: Alphabetically, ranked on the "contextual value added" score, and ranked on the combined or "aggregate" score achieved in the three tests - the maximum possible being 300.

In the rankings, where more than one school has the same score, they are further ranked on the average points scored by pupils (see below for more on how this is calculated).

In the alphabetical LA lists, after the school's name, the first column of figures shows its value added score, then the aggregate score, then the average number of points achieved by pupils.

The results relate to the percentage of the pupils eligible to take the tests who achieved Level 4 or above - the standard expected for their age.

In the contextual value added ranking (CVA), the bold column shows schools' scores.

A CVA score is worked out for each pupil by comparing their Key Stage 2 performance with the middle performance of other pupils with similar prior attainment at Key Stage 1.

The arithmetic mean of these individual scores gives a score for the whole school. This is converted to a number based around 100.

Note: the resulting rankings need treating with care. Official statisticians say the significance that can be attached to different scores depends on various factors, including the numbers of children involved.

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

In the Aggregate (AGG) ranking, the bold column shows the aggregate score on which it is based.

This is a number out of 300 but is not simply the sum of the percentages of pupils achieving the expected level in each subject.

It is derived from the number of pupils achieving at least the expected level, divided by the number eligible to take the test, for each subject, added together and multiplied by 100.

The letters SS signify a small school - with fewer than 11 pupils eligible to take the tests. They are included in the alphabetical lists for completeness but no results are published for them.

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Anyone care to try and explain that lot?