In September last year, our Commission on Accountability, organised by the NAHT, published the report Improving School Accountability. In it, we set out seven ways in which the current accountability system is having a negative impact on schools. The commission concluded that, overall, the way in which government and Ofsted were holding schools to account was doing more harm than good.

The commission set out nine recommendations for change that would strike a better balance between holding schools to account and helping them to improve. We concluded that arrangements that had lifted the system to good over the last 25 years would not push us on to great over the next quarter of a century and that we risked becoming anchored to average internationally unless there was some loosening of the strait-jacket on good schools.

The changes to inspection set out today by Ofsted have been described by the chief inspector Amanda Spielman as an evolution, not revolution, and – having read the draft handbook – I think that is an apt description. However, in light of the seven ways in which accountability can do harm, proposals for change fall far short of being a gamechanger:

Firstly, the four-point scale from outstanding to inadequate remains in place and school effectiveness will continue to be boiled down into a single adjective for public consumption. The overall effectiveness judgement is loaded with such importance to the future of a school that it can overshadow everything else that might take place on inspection.

Worse still, with such high stakes attached, our Commission found that the desire to achieve or maintain an Ofsted grade can drive a compliance culture, prompting schools to focus on meeting the inspection criteria rather than becoming the very best that they could; to play it safe rather than to innovate or push boundaries.

Secondly, Ofsted continues to spread itself too thinly, and there are serious questions about the manageability of proposed arrangements. The Accountability Commission previously argued that Ofsted was no longer well placed to provide a qualitative judgement on how good a "good" school actually was, that they should abolish the outstanding grade and focus their limited resources on providing a stronger diagnostic insight to schools that were struggling.

This recommendation was not accepted by the inspectorate. Yet within the evaluation criteria of the new inspection handbook, Ofsted has been unable to adequately distinguish between good and outstanding. Language used to describe "outstanding" is subjective and imprecise, with an overuse of adjectives to describe curriculum excellence such as ‘strong’ and ‘ambitious’. In places, evaluation criteria appear vague to the point of unusable. I would not want to be an inspector trying to use it to justify one judgement over another.

The leadership and management section of the new inspection handbook is particularly concerning. The distinction between "good" and "outstanding" leadership has been whittled down to just three additional criteria: that leaders ensure teachers receive highly effective professional development; that meaningful engagement takes place with staff to identify workforce issues; and that staff well-being is good. These are no doubt worthy activities.

But what a depressingly unambitious view this is of what the best leadership in our schools should be. Compare this to the current framework and it appears that we are moving backwards. This further supports the view of the commission that under the weight of accountability, leadership priorities and behaviours had become skewed and that too often we have lost sight of what great leadership is.

Thirdly, despite the clear intent from chief inspector Amanda Spielman to ensure schools serving challenging communities are treated fairly at inspection, it is far from clear within these proposals how new arrangements will actually level the playing field. It appears that hope for greater fairness rests in the ambiguity found within the evaluation criteria and belief that inspectors will apply sensible professional judgement.

However, elsewhere in the ,handbook it appears there is an apparent toughening up of expectations, for example, that all children, irrespective of starting points, will achieve or exceed age-related expectations in reading. This will surely make it even harder for schools to be recognised as doing an effective job where pupils have lower starting points. The Commission recommended that Ofsted should start using comparative performance data, using families of schools groups, to provide like-for-like comparisons between schools to inform fairer judgements of effectiveness, irrespective of circumstance. There is no reason why this could not be introduced within the new framework for September.

Everything may be different but I fear little of substance has changed.

Undoubtedly, the new framework has potential to be an improvement on current arrangements, though there is a lot of work to do between now and the start of inspections from September to realise this. Some may therefore consider it unfair to judge the shortcomings of new proposals harshly. It was, after-all, only intended to be an evolution of current arrangements and Ofsted is constrained in what it can change within the parameters that have been set for them by ministers.

The uncomfortable truth, for Ofsted and the government, is that we will not succeed in transforming standards and turning more good schools into great schools, by taking a variation of the same top-down approach to accountability of the last 25 years. We need to be more radical than that, perhaps more revolutionary than evolutionary, if we truly desire to be counted amongst the leading education systems in the world.

Nick Brook is deputy general secretary of the NAHT headteachers' union, and chair of NAHT's accountability commission