Free schools are the best performing type of secondary schools on the government’s preferred Progress 8 measure, new figures have shown.

The 53 free schools included in today’s GCSE league tables had an average Progress 8 score of 0.15 last year.

Today’s statistical release from the DfE warns that the numbers of free schools “are too small to allow robust conclusions to be drawn about their performance at the end of key stage 4, or compare between years”.

However, the results cheered free-school champions.

Progress 8 aims to capture the progress pupils make between the end of primary school and taking their GCSEs. A score above zero means a school is making above average progress, and a school is judged to be below the floor standard if its Progress 8 score is below -0.5.

A spokesman for the New Schools Network, a government-funded charity that supports free schools, said: “These results are a ringing endorsement of the free school policy. Some of the best results in the country are coming from free schools and there are three times as many in the most deprived parts of the country as the least deprived.”

He added: “It is not surprising that the prime minister wants more free schools in the most disadvantaged areas of the country. They are proving to be the most effective way of transforming children’s life chances and promoting social mobility across the country.”

Sponsored academies - usually underperforming schools that were taken over by an academy trust to improve their performance - performed worse on average than non-academies.

For sponsored academies, the average Progress 8 score was -0.12, compared to -0.06 for local authority maintained mainstream schools.

Converter academies had an average Progress 8 score of 0.10.

For university technical colleges (UTC), the average was -0.86, for studio schools it was -0.68, and for further education colleges, it was -2.10.

The statistical release warned about the small number of UTCs and studio schools, and highlighted the fact that their pupils usually join the institutions at the start of key stage 4, so will typically have spent only two years at them by the time they take their GCSEs.