Chief regulator Glenys Stacey says Ofqal has noticed a pattern in appeals of exam results from schools.
The analysis that we have done has shown that there is tactical appealing at critical grade boundaries - C/D at GCSE and B/A at A-level, that doesn't mean that every appeal at that boundary is tactical, but you can see from the pattern that it would suggest there is tactical appealing.
Secondly, the way the appeal system is designed at the moment, and indeed headteachers agree with us, that where you're within a couple of marks of such a grade boundary it's worth appealing because it is a one-way bet.
Schools are playing the exams system by appealing against results in a bid to improve pupils' grades, the qualifications regulator has said.
Ofqual suggested the current GCSE and A-level appeals process was designed for a "more innocent era" and is being tactically used by teachers under pressure to secure good results.
In a new report it said that evidence suggests an increase in appeals against results, particularly those that are within one or two marks of key grade boundaries - such as C/D at GCSE and A/B at A-level.
It also found that examiners dealing with appeals may be looking for extra marks to award to students as they are conscious that the final result could have a major impact on a youngster's future.