David Cameron will today announce plans to open another 500 free schools.
Justifying his decision, he will claim that "academies and free schools are most likely to be good or outstanding," adding that they "do not just help the performance of their pupils, but pupils in surrounding schools".
But are either of these claims true?
Let's look at academies first. Are these really any more likely to be good schools?
There are two types of academy schools. The first type are sponsored academies. These are typically failing schools which have been turned into academies following government intervention. According to Ofsted, in December 2013 56% of sponsor-led academies were good or outstanding. This compares to 78% of all schools nationally. So what about the rest?
The second type are converter academies. The problem with assessing the performance of these schools is that the majority were already judged to be good or outstanding before they were allowed to convert. It is therefore hardly surprising that they should remain good or outstanding once converted.
However some of these schools have not. In fact several witnesses reported to the education select committee that these schools have a tendency to go "off the boil" once they are given independent status. Further analysis by the National Foundation for Educational Research found "no significant difference in attainment progress after two years between converter academies and similar non-academy schools".
In a report released earlier this year, the commons education committee also found "no convincing evidence of the impact of academy status on attainment in primary schools", adding that while "some chains such as Harris have proved very effective at raising attainment… others achieve worse outcomes than comparable mainstream schools".
"What is clear is that the picture is highly variable across the country and, in the case of sponsored academies, across chains."
The picture with free schools is even less clear. Most free schools have only been open for relatively short periods of time so it is difficult to draw any firm conclusions about their performance.
As Ofsted concluded last year, it is simply "too early to judge the overall performance of free schools". The commons education committee reached the same conclusion this January. However, analysis of Ofsted inspections last year found one in three free schools failing to meet required standards compared to just 19% of all schools.
However, the lack of any convincing evidence to prove the impact of free schools and academies is not stopping the prime minister and his allies pushing ahead.
Today Policy Exchange release a report timed to coincide with the prime minister's speech. Titled 'A rising tide: The competitive benefits of free schools', the report claims "free schools are raising standards for other pupils across the local community, especially in some of the poorest performing schools". It goes on: "The paper finds that competition is driving up standards at both primary and secondary level.
However, buried in the report is an admission which fundamentally undermines its entire basis. According to the authors:
"It should be obvious – but bears setting out explicitly – that such data cannot demonstrate conclusively that any changes seen are as a response to the new free school.
"A school appointing a new head; a change to academy status; a glut of teachers leaving; a financial crisis – all of these can affect an individual school for better or worse. It should also be remembered that sample sizes in some of these categories is quite small, and correlation should not be mistaken for causation."
In other words the central claims of the report - that free schools push up standards in the surrounding areas - isn't backed up by the evidence.
Commenting on the admission today, co-founder of the Local Schools Network Henry Stewart said:
"David Cameron is basing a major policy on claims for free schools that are not backed up by his own report. For primary schools, the report certainly does not show that free schools result in nearby schools improving.
"To use these figures to justify more funding of free schools shows a basic lack of understanding of the data."
As Ofsted and MPs have also concluded, it is just too early to judge whether free schools push up standards. Maybe they do and maybe they don't. The fact is we just don't have sufficient evidence yet.
With the education budget set to be extremely tight in the next parliament, it is vital that all funds are spent on policies where we have concrete evidence that they can make a difference.
David Cameron simply does not have that evidence on free schools.