As secondary school league tables for England are published, we take you through the key points.
What do the league tables tell us?
They look at the performance of schools as measured through a detailed, statistical look at pupils' progress, called Progress 8.
Although the formula is quite complicated, its aim is very simple - to check that pupils are making as much progress as they are capable of, given their level of ability when starting secondary school.
Pupils' actual achievements in eight GCSEs are plotted against their expected achievements. Expected progress is charted according to their results at the end of primary school.
The results are amalgamated, and schools are then bracketed into five bands, ranging from well above average to well below average.
This method is being used for the third year running, and is a long way from the days of top and bottom school performers based solely on raw results.
So don't the league tables look at the GCSE results on their own any more?
Yes they do, but the days of simply measuring a school's success or otherwise by raw GCSE results are long gone.
The Department for Education (DfE) also uses another measure called Attainment 8, but this is secondary to Progress 8.
Attainment 8 focuses on the results across individual pupils' best eight subjects.
But they are not just any old subjects - English and maths are compulsory and worth double points.
Then there is the choice of three subjects from the English Baccalaureate (core academic subjects), and any other three from the DfE's approved list of qualifications - including vocational qualifications.
How should I interpret Progress 8 scores?
Progress 8 scores generally fall somewhere between -1 and 1.
The number is then placed into one of five bands:
- well above average
- above average
- below average
- well below average
It is these bandings which will be of most use to parents.
Why eight subjects?
The short answer is that it is considered fairer to see a pupil's best achievement across a broad spectrum of subjects.
Teachers and head teachers had complained that the "five good GCSEs" measure, used until the academic year 2014-15, was way too narrow.
They also argued that the English Baccalaureate measure was too prescriptive, and relevant only for the more academic students.
So the aim of Progress 8 and Attainment 8 is to give a broader picture of how schools are bringing their pupils on.
With the new 9-1 grading system, what is now considered a pass?
Individual pupils pass a GCSE if they get a grade 4 or above.
But for the purposes of the school performance, the DfE uses grade 5.
This reflects the conflict between the wish to bring GCSE standards up to those of certain high-performing nations when they were changed, and the need to remain fair to the first few sets of pupils who sat these new-style examinations.
Head teachers have said that effectively having two pass marks can cause confusion.
What happens elsewhere in the UK?
Data on how well Scottish pupils do in reading, writing and numeracy is published as part of its Curriculum for Excellence.
The Welsh Assembly publishes school performance information in the form of a colour code. Schools are rated green, yellow, amber or red, according to how well they are performing.
School league tables are not published in Northern Ireland.