School leaders have called on Ofsted to publish the training material and criteria inspectors will be using under its new framework.
Senior figures from both the Association of School and College Leaders and the NAHT headteachers’ union have said schools should be given more information about how the inspectorate makes its judgements when looking at lessons and pupils’ work.
NAHT deputy general secretary Nick Brook warned that schools are working in a system of "haves and have nots" because those school leaders who work for Ofsted as inspectors have a greater insight into how the inspectorate reaches its judgements.
Both unions have said providing transparency over inspection training will prevent myths developing in schools about what is expected when the new system starts in September.
Inspection: How Ofsted plans to deep dive into subjects
However, Ofsted has said school leaders do not need to do anything to prepare for the new framework other than read the new school inspection handbook.
The inspectorate's new framework has an increased focus on curriculum and includes a new quality of education grade.
Mr Brook said that as Ofsted moves to a new system it should publish the training material inspectors have been given.
He said: “Schools should be able to know what inspectors want to see and what inspectors don’t want to see.
“People who work for Ofsted as inspectors will receive this training and have the inside track on what inspectors are looking for under the new framework which they can take back to their schools.
"When it comes to inspection, ours is a system of ‘haves’ and ‘have-nots’, where some schools have considerably greater understanding of what to expect from inspection than others.
"This is an issue that is rarely raised, because it is as it has always been. From the moment serving school leaders were invited to take part in inspection this has been an uncomfortable tension.
"The problem is that becoming an inspector is an opportunity that is closed off to some school leaders. If you work in a school that has been judged less than good you are unlikely to meet entry requirements, according to Ofsted’s inspector specification."
An Ofsted spokesperson said: “If schools want to know more about how inspectors will go about inspection, they can read the note Inspecting the curriculum, which sets this out clearly.
“We held our biggest consultation ever on the education inspection framework, and have been very open in its development. And there will be more opportunities for school leaders to talk to Ofsted about it at conferences and webinars in the future.”
Questions have been raised about how Ofsted will judge the curriculum after it published research into the use of lesson visits and work scrutiny to assess the curriculum.
Ofsted’s new inspection framework places an increased emphasis on the curriculum throughout a new quality of education grade which will also take into account teaching and learning and pupils’ results.
Ofsted has said it will look at the intent, implementation and impact of a school’s curriculum.
Research it published last month showed that inspectors looking at lesson visits and work scrutiny had substantial reliability in the judgements they reached at primary schools.
However, these inspection methods were less reliable at secondary school in assessing the curriculum and teaching.
Daniel Muijs, Ofsted’s deputy director for research and evaluation, said this was because inspectors were "looking at lessons outside of their subject expertise."
To address this, Ofsted is providing subject specific guidance to inspectors to improve the reliability of secondary school inspections.
Stephen Rollett, ASCL’s inspection specialist, said: “Ofsted has produced a methodology document which outlines how it will carry out deep dives into subjects, but this doesn’t include the detail of any final rubric they will be using when they look at pupils’ books and lessons.
“Ofsted’s research into work scrutiny and lesson observation implies that using an appropriately crafted rubric is one way to help improve the validity and reliability of these practices.
“If such a rubric is created to support inspection it should be published in the interests of transparency. This will help to stop new myths emerging.
"Also, around 70 per cent of Ofsted inspectors work in schools and it would not be appropriate for them to have access to it while other schools didn’t.”
The inspectorate has attempted to stop new inspection myths developing around its new framework.
It has told schools they do not need to write curriculum intent statements or restructure their staff to prepare for Ofsted’s new inspections.