Academies in Merton have seen a fall in the number of pupils achieving five good GCSEs which is not reflected across other schools. 

The percentage of pupils achieving five GCSEs at A* to C at Harris Academy Merton dropped from 74 per cent to 58 per cent between 2013 and 2014, according to government figures published last week. 

St Mark's Church of England Academy in Mitcham saw a much smaller fall in results, from 52 per cent to 49 per cent in the same period, putting the school below the national average of 56.6 per cent for state-funded schools.

The results come after a cross-party government report earlier this month argued it was too early to argue whether academies improve standards.

A spokesman for Harris Academy Merton said the statistics for 2014 and 2013 should not be compared because of changes to GCSE exams.

In 2014 students were not able to take or resit exams during the year. Instead, all students were examined at the end of the two-year programme.

"In addition, Harris Academy Merton has been introducing a more academic curriculum to ensure that students earn qualifications in subjects that appeal most to employers and universities," the spokesman said.

"What the league tables do show is that our students make excellent progress when they join us from primary school. Our focus is now on ensuring that this progress leads to a larger number of high GCSE grades this year."

The school's results have fluctuated since 2011, with a similar drop of more than 10 per cent in good GCSE grades between 2011 and 2012, bouncing back to 74 per cent in 2013.

Harris Academy Morden achieved similar results last year, with 56 per cent of pupils achieving five A* to C grades. Results were not available for 2013.

St Mark's Church of England Academy in Mitcham declined to comment on the school's results.

Councillor Martin Whelton, Merton Council's cabinet member for education, defended the academies' track records, pointing out that only 25 per cent of pupils were achieving five A* to C grades 10 years ago.

He said the results would not impact on Harris Academy Federation's bid to provide a third secondary school in Merton.

"We know they have got a positive track record in the schools that they run across the borough", he said.

Wimbledon College also saw a drop in A* to C grades at GCSE level, down from 80 per cent to 72 per cent.

But headteacher Adrian Laing said the school's results were not affected by changes to the exams format because pupils have always sat exams at the end of two years of study.

He said: "Very simply it was our cohort. It was nothing to do with examination changes...The boys came in at a lower level than the previous year and they have made more progress than the previous year."

Overall, 64 per cent of Merton pupils achieved five good GSCEs, putting the borough in the top 20 local authorities in England.

Merton was the only council in London to see improved GCSE results in comparison to the previous year.

To see more figures for Merton schools, visit the Department for Education's website.