Schools naturally want to show their exam results in the best light. But the recent GCSE and A-level results tables published in some newspapers are selective. The first set of national data from the Department for Education is not due out until the autumn.

But parents, be warned. The blizzard of statistics is about to get thicker because the government is introducing new criteria to evaluate school performance.

Until now, the main yardstick has been the number of children attaining at least five GCSE passes at A*to C including maths and English. This presents achievement across a broad spread of pupils. But it does not reveal what percentage get As or A*s, or take into account the ability of pupils when they started the school.

So two new measures are coming into effect, called Attainment 8 and Progress 8. The progress figure will be a successor to the current value-added score and is meant to reflect how far pupils have come from the end of primary school to GCSE.

"If the Progress 8 score is zero, that means the pupils would have made the expected progress," explained JFS headteacher Simon Appleman. The intention behind it, he believed, was "very good. A school which has a weaker cohort on entry gets recognised for their progress."

Attainment 8 will succeed the 5 GCSE-figure. It will comprise a basket of eight subjects: maths and one English; then three of the more traditional academic subjects where the student has done best such as science, history or a language: and then three other GCSEs. Maths and English will count double. The overall score will then be divided by 10 to produce an attainment figure.

So JCoSS , one school which has already opted for the calculation of an Attainment 8 mark based on last year's results, scored over 60, which means the average grade was just over a B.

Its Progress 8 score for 2015 was 0.57 - a good score, indicating that its pupils last year achieved on average half a grade higher at GCSE than would have been predicted on entry in their first year.

But this is not all for parents, pupils and teachers to get used to. From 2017, A* to G are being phased out and instead pupils will be graded from 9 to 1, with the current A* band divided into 9 and 8, and 5 being a good pass. English and maths will be graded by the new numbers next year, with other subjects to follow in 2018.

The curriculum has also been reformed and maths, according to Mr Appleman, will become harder. Some topics previously in the further maths GCSE course have now gone into the foundation maths paper.

That is a lot of change to cope with in a short space of time. Where teachers were familiar with the old boundaries between A, B or C grades in exams, now they are going to have to readjust to the new system.