I know Ofsted is unlikely to win any popularity contests. Inspectors pass judgement on the work of others and, in doing so, are always going to be the subject of intense scrutiny.

I accept that, and acknowledge the pressures that inspection and accountability inevitably bring. I also accept that Ofsted doesn’t always get it right in the 30,000 inspections we conduct each year. However, when poor inspection practice is identified, senior inspectors always deal with it promptly, as they did last year when some reports did not adhere to our revised guidance on judging the quality of teaching.

Of late, however, I believe criticism of Ofsted has been overdone and has been used as a way of deflecting attention away from underperformance and failure. Too often, the charge of inconsistency has become a Pavlovian response to unfavourable inspection outcomes. It’s an easy charge to level, but that doesn’t always make it valid. Judgements about schools with similar outcomes can vary for a variety of reasons: the relative performance of different groups of children, declining standards of behaviour, turnover of staff and frequent changes in leadership. Dig under the surface of an apparently inconsistent judgement and you will probably see that the inspector has made the right call. If this weren’t the case, we would not have, year after year, a 91 per cent satisfaction rating from the institutions we inspect.

I appreciate how hard it is to see colleagues who give so much to the school judged coolly by strangers who inspect for a couple of days and find them less than perfect. Teachers work with passion. Inspectors have to deal in detachment. It can make for an uncomfortable cultural fit.

But that doesn’t mean the default position should be to condemn the judgement given - or the person delivering it. Too often people find it easier to shoot the messenger than to take a long, hard look in the mirror.

In some parts of the profession, there seems to be a growing trend of attributing every disappointing judgement - special measures, requires improvement or even missing out on outstanding - to inconsistency on the part of the inspectorate. At the same time, much of the criticism that we face is often contradictory. In last week’s TES, for instance, in one article we came under fire for running a system that was too dependent on the vagaries of which inspector happened to call (“Does your grade depend on the inspector you get?”, 21 November) and in another for running a system where all judgements were predetermined by the available performance data (“My vision for a better Ofsted relies on trust”, Comment). I’m not sure our critics can have it both ways.

`Continually evolving’

These accusations betray a fundamental lack of understanding of how Ofsted goes about school inspection work. The sample of schools selected for inspection in a given year is carefully considered. Ofsted does not inspect all schools across England with the same regularity, but instead uses a risk-based approach when deciding whether and when to inspect. The frequency of inspections is based on the outcome of the previous inspection, the time elapsed since and the current performance of the school. Selection is not a random process.

Neither are inspectors deployed randomly on a “taxi rank” basis. Individuals with the right skills and expertise are chosen to inspect relevant schools. More than 1,000 of our additional inspector workforce are current practitioners and around 60 per cent of inspections now have a teacher on the team.

And that’s not the end of our commitment to high standards. Our quality assurance process is detailed and continually evolving. Inspectors undertake quality assurance visits in more than one in 10 inspections. Monthly consistency meetings are held across our regions and we take a robust approach when the process reveals poor practice - a number of additional inspectors have had their lead inspector status removed after concerns about performance.

Ofsted places the highest importance on ensuring that its inspection judgements are reliable for parents, pupils and schools. The knowledge and expertise of our inspectors is integral to our performance and we are continually looking for ways to improve and build on our commitment to achieving the highest standards in school inspection.

This is why, from September 2015, we will be contracting with all inspectors directly and bringing the services they provide in-house, not via a third party. We believe this will allow us to ensure an even higher quality of inspections, particularly by encouraging more serving practitioners in education to get involved in inspection. This, we believe, will be another vital step towards a self-improving education system for England.

As I have said on many occasions, the profession must take more ownership of inspection. So let me make a direct appeal to TES readers: if you are a senior leader at a good or outstanding school, consider joining Ofsted on a part- or full-time basis.

At the same time, we are looking to make radical changes to the way we inspect. We are in the middle of consulting on plans to introduce frequent but shorter inspections for good schools and colleges. These will have a much clearer focus on ensuring that high standards have been maintained.

In particular, inspectors will be looking to see that headteachers and leadership teams have identified key areas of concern and have the capability to address them. For good schools that can show they have the capacity to maintain and improve performance, the changes proposed will mean there is no longer any need for a full inspection. They will make the inspection experience less “cliff-edge” and allow good leadership teams to demonstrate how well they know their own schools.

I also hope that an additional consequence of these important reforms will be a reduced tendency on the part of the profession - to borrow a football analogy - to go for the man and not the ball when reacting to inspection findings.

Sir Michael Wilshaw is Her Majesty’s Chief Inspector. Ofsted’s consultation on the future of education inspection runs until 5 December. Find it at www.ofsted.gov.ukfutureofinspection