The exams regulator Ofqual has warned "all players" in the system against making "knee-jerk" reactions to this summer's GCSE results.
This is the first year pupils have sat the new style GCSEs in English and maths, with harder content and 9-1 grades.
Speaking at a symposium in London this afternoon, chief regulator Sally Collier said that the overall results should remain stable, but individual schools could experience more variation than normal.
Speaking to Tes, she said: "For example, if a school whose results have been very stable for years and on an upward trajectory, and you suddenly get an unexpected set of results, you would expect Ofsted or whoever to say, 'hang on a minute, why has this happened?'. Our message is to stop and reflect on why that has happened."
She said Ofqual has given this message to Ofsted, regional schools commissioners, the Department for Education and the National Governance Association.
More English entrants
The audience was also told that examiners have been told not to penalise students taking closed book exams who made small mistakes when repeating quotes from texts.
The event heard that changes to the accountability measures, such as the removal of international GCSEs and the introduction of Progress 8, had increased the numbers of students entering English GCSEs.
This has changed the cohort and, because more lower ability pupils were now taking the literature exam, the overall proportion getting top grades this summer was expected to fall.
Ms Collier also said that, Ofqual would investigate all the errors in this summer's exam papers at the end of the summer, taking stock of any lessons to improve the system.