The Key Stage 1 to 2 CVA measure

What is Contextual Value Added?

What do we mean by CVA?

Some pupils will find it particularly difficult to reach the level expected for their age in assessment tests e.g. because they have significant special educational needs (SEN). But all pupils are capable of making progress and it is important that schools are given recognition for the work that they do with all their pupils. Measures of absolute attainment therefore need to be complemented by measures of the progress made by pupils - the value added - from one key stage to another.

Value Added (VA), which was first published in the Primary School (KS2) Performance Tables in 2003, did this by comparing the results achieved in Year 6 against a pupil's starting point (or prior attainment) - the results of KS1 assessments in Year 2.

CVA is not very different from VA. The basic principle of measuring progress from the KS1 to KS2 remains the same. However, a number of other factors which are outside a school's control, such as gender, special educational needs, movement between schools, and family circumstances, are also known to affect pupils' performance.

CVA therefore goes a step further than VA by taking these factors into account and thus gives a much fairer measure of the effectiveness of a school. This means that CVA gives a much fairer statistical measure of the effectiveness of a school and provides a solid basis for comparisons. Nevertheless, no single measure of performance can tell the whole story about a school's effectiveness and CVA must not be viewed in isolation. Attainment data continues to play an important role in painting the full picture of a school's performance.

Calculating the Contextual Value Added scores

We base each pupil's CVA score on a comparison between their actual KS2 performance and the KS2 performance predicted for each pupil by the CVA model, having taken into account the range of factors affecting performance.

An average of all pupils' CVA scores is produced for a school. That average is adjusted by the CVA model to account for cohort size, which then produces a school level CVA measure. This number is presented as a number based around 100 and indicates the value the school has added on average for its pupils.

Ready Reckoner

The Tables website provides a CVA Ready Reckoner as an additional tool which allows you to look at the detailed calculations. It can be found within the CVA guidance section at www.education.gov.uk/performancetables

Coverage of CVA

CVA covers all maintained schools and non-maintained special schools. CVA models have been produced separately for mainstream schools and special schools.

Interpretation of a school's CVA score

The CVA section shows, for each school:

• the KS1-KS2 CVA score
• the upper and lower limits of a 95% confidence interval
• a coverage indicator.

The coverage indicator shows the percentage of pupils at the end of KS2 included in the CVA calculation. This might not be 100 per cent because we do not have the KS1 test results for some pupils, for example because they were previously educated outside England.

If the coverage indicator is very low (below 50 per cent) then the CVA score is not published because it does not properly represent the effectiveness of the school.

The CVA measure is shown as a score based around 100. Scores above 100 represent schools where pupils on average made more progress than similar pupils nationally, while scores below 100 represent schools where pupils made less progress.

What a school's CVA measure tells you

For KS1-KS2 CVA, a measure of 101 means that, on average, the school's KS2 cohort has achieved one term's more progress than the national average. A score of 99 means that the school's pupils made a term's less progress.

While the CVA measures give an indication of overall effectiveness, the significance that can be attached to any particular school's CVA measure depends, among other things, on the number of pupils included in the CVA calculation. The smaller the number of pupils, the less confidence can be placed on the CVA measure as an indicator of whether the effectiveness of a school is significantly above or below average.

Confidence Intervals

The CVA measure is a statistical means of assessing the relative effectiveness of school or pupil progress between KS1 and KS2.

CVA is, however, based on a given set of pupils' results for a particular test paper on a particular day. A school could have been equally effective and yet the same set of pupils might have achieved different results on the day. And the school would almost certainly have shown slightly different results with a different set of pupils, even with the same levels of prior attainment.

Hence, although the CVA is based on all pupils in the school cohort, not just a sample of them, this degree of uncertainty should be taken into account if interpreting the figures as estimates of a school's effectiveness.

The uncertainty of a CVA score as a measure of school effectiveness can be presented as a confidence interval (CI). This is a range of scores within which we can be statistically confident that the “true” school effectiveness will lie.

The degree of significance that can be attached to a school's CVA measure depends, among other things, on the number of pupils included in the calculation.

The CVA methodology produces a 95 per cent CI to show the range within which we can be confident the CVA measure represents the overall effectiveness of a school. If a school cohort is large the width of the CI will be small, but if a school cohort is small the CI will be wide.

A school level CVA measure must always be interpreted alongside the CI. Schools where the lower limit of the CI is above 100 represent schools where pupils on average made significantly more progress than pupils nationally, while schools where the upper limit of the CI is below 100 represent schools where pupils made significantly less progress.

Examples for KS1-KS2 CVA:

• a measure of 100.6 with a CI between 99.8 and 101.4 means the progress made by pupils in the school's KS2 cohort is not significantly different from the national average
• a measure of 101.5 with a CI between 100.9 and 102.1 means the progress made by pupils in the school's KS2 cohort is significantly above the national average
• a measure of 99.2 with a CI between 99.0 and 99.4 means the progress made by pupils in the school's KS2 cohort is significantly below the national average.

Further information on calculation and interpretation of CVA measures and confidence intervals can be found in the “Technical Guide to Contextual Value Added 2007 and 2008 Model” on the website at www.education.gov.uk/performancetables

Contextual Value Added (CVA) Percentiles

The CVA percentiles give the distribution of CVA scores and show where schools are placed nationally compared to other schools, based on the CVA measure. There are three versions, which allow comparisons against: all schools (i.e. both mainstream and special); mainstream schools only; and special schools only.

Key Stage 1 to Key Stage 2 CVA Measure (centred around 100)
Profiles			Percentiles
All Schools	All Maintained Mainstream Schools	All Special Schools
101.5 and above	101.5 and above	102.2 and above	Top 5% of schools nationally
100.6 to 101.4	100.6 to 101.4	100.0 to 102.1	Next 20% of schools nationally
100.2 to 100.5	100.2 to 100.5	99.6 to 99.9	Next 15% of schools nationally
99.7 to 100.1	99.8 to 100.1		Middle 20% of schools nationally
99.4 to 99.6	99.4 to 99.7		Next 15% of schools nationally
98.5 to 99.3	98.5 to 99.3	99.1 to 99.5	Next 20% of schools nationally
98.4 and below	98.4 and below	99.0 and below	Bottom 5% of schools nationally

Note: For Special Schools, the scores in the middle three bands are very close. They have therefore been combined into a single band representing the middle 50% of schools.

Snake plots are a useful way of presenting percentiles. The following three plots simply repeat the information shown in the table above, but in a way that enables the national distribution to be more easily understood.

All schools KS1-KS2 CVA Scores and Ranks

All maintained mainstream schools KS1-KS2 Scores and Ranks

All special schools(including non-maintained) KS1-KS2 CVA Scores and Ranks