This year’s GCSE results day will be more nerve-jangling than ever for school leaders in England, who have an anxious wait to see how their school and their careers will be judged under the government’s new performance measures.

Out goes the old measure, which ranked secondary schools on the proportion of pupils gaining C grades or higher in five GCSE subjects including English and maths. It has been replaced by a new value-added metric known as Progress 8 – applauded by many as a big improvement but which has problems of its own.

The end of the old measure means schools can finally be rid of the dreaded C/D borderline. Because only grades C and above counted towards passing the government’s floor target of 40%, pupils expected to get Ds received more attention in an effort to haul them up to Cs, especially in the compulsory maths and English subjects.

Gaming the old system abounded: until the Department for Education blocked the tactic, schools would enter pupils early and often for exams to get the sought-after C. A cottage industry sprang up in guiding schools towards different subjects and more exotic options, according to perceived difficulty, until some were blocked by the DfE or Ofqual, the exams watchdog.

More able students also suffered. Since the old measure gave no reward to schools that improved their pupils from C grades to Bs or As, schools had little incentive to support any student once they were likely to get a C. The same logic applied to those likely to gain grades E and below. From this year, all that changes, thanks to the DfE’s adoption of Progress 8, which as its name suggests measures progress in attainment rather than setting a simple bar.

“I think it’s a fantastic improvement,” says Rebecca Allen, director of the Education Datalab research unit. “It incentivises schools to offer a good curriculum and lets them focus on all students, from the top to the bottom.”