A year-long Tes Scotland investigation has forced the schools inspectorate, Education Scotland, to publish the date of the last inspection for every school in the country - and prompted a debate on whether school inspections really matter.

Our figures - which showed that some schools had not been inspected for 16 years and more than a fifth of all schools had not been inspected for over a decade - were picked up by the national press and resulted in first minister Nicola Sturgeon being grilled by Scottish Conservative leader Ruth Davidson last week. Davidson said that school inspections had “crashed to their lowest level since devolution” and noted that, of those not inspected for at least a decade, one was in the first minister’s constituency and two were in that of education secretary John Swinney.

But Scotland’s largest teaching union argues that opposition politicians are calling for inspection for its own sake. EIS general secretary Larry Flanagan says there is no evidence that inspection improves outcomes for pupils and believes Scotland should follow in the footsteps of Finland, where there is no school inspection regime. At the very least, he argues, Education Scotland should move from inspecting individual schools to scrutinising entire council education services instead. That would “impact across all the schools in that local authority”, whereas messages from individual school inspections do not necessarily “trickle out to other schools”, he says.

“All inspection does is largely confirm what people know already,” adds Flanagan.

Keir Bloomer, convener of the Royal Society of Edinburgh’s education committee, says the public and the media tend to think that inspection is a good thing without being very clear about why. Both Bloomer and Lindsay Paterson, professor of education policy at the University of Edinburgh, say there is little research evidence about inspections’ impact.

Bloomer says: “Do schools that have recently been inspected improve faster than others? This has never been examined in Scotland.”

Tes Scotland asked Education Scotland what evidence there is that inspection improves outcomes for pupils. Inspections and improvement go hand in hand, says a spokesman. “These [benefits] include providing schools with a clear sense of direction, providing additional evidence to support improvement, increasing the pace of change in existing improvement work and increasing staff confidence in their professional skills.”

But when it comes to hard evidence to support these claims, all the body cites is its own post-inspection survey of headteachers. This received just 41 responses but 90 per cent of those heads reported that their school had made changes as a direct result of the inspection, while 95 per cent said professional dialogue with inspectors had helped their school to make improvements.

The spokesman adds: “Education Scotland monitors both international and national research evidence about the impact of inspection.” It is a member of the Standing International Conference of Inspectorates, which is this year focusing its research on “Impact of Inspection”.

However, Paterson agrees that the most likely impact of inspection - based on the scant evidence - is that it leads to improvement by encouraging self-evaluation and concentrating teachers’ attention on improvement and how to measure it. So we should care about the frequency of inspection, he argues, because we need more of it if we want that focus on improvement. He also says that these visits need to have “more emphasis on dialogue and advice, and less on measuring standards”.

This comes as changes are being proposed by Scotland’s former chief inspector of education, Graham Donaldson, in Wales. Donaldson’s review of the Welsh inspectorate Estyn, as well as recommending inspection should be suspended for 2019-2020 to give schools space to introduce the new curriculum, also says the focus should be on school self-evaluation and the body should no longer give headline rankings.

Meanwhile, Flanagan says the EIS receives far fewer complaints about the stresses and strains of inspection than in the past. Now teachers are far more likely to complain that the professional dialogue that is supposed to happen during inspection is “superficial”, says Flanagan. “Teachers should be engaged in the process, not simply observed,” he adds.

Dr Melanie Ehren, of the UCL Institute of Education’s Centre for Educational Evaluation and Accountability, has researched the impact of inspection. She says that where an inspection regime such as that in Scotland has been in place for a long time, “efficiency” reasons partly explain inspections becoming less frequent. However, she says another factor is that standards and expectations have often had time to bed in and become well understood. Ehren says that regular inspection is still important, however, as it “reinforces expectations and the standards on quality”.

Yet she notes that, like Finland, Austria also recently scrapped its inspection regime, as did Germany, because they “did not see impact”.

There is no sign of such a move in Scotland, where the Scottish government has made it clear that it plans to increase inspection by a third to 250 inspections a year in 2018-19.

Bloomer, therefore, concludes that Scotland seems set to “muddle along spending quite a lot of money on a system without clear objectives and no success criteria”.