It would take Ofsted more than 80 years to assess all the country’s multi-academy trusts under the current rate using its new system for checking on the academy chains.
Tes can reveal that the inspectorate will check on the performance of just a dozen MATs this year under its new summary evaluations.
Ofsted said it only had the resources to assess 12 MATs a year but would be open to increasing this if it was given more funding to do so.
The new inspection plan was launched to give the watchdog an accurate picture of how trusts operate by looking at a "broad range" of MATs.
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However, the figures revealed today suggest that Ofsted will only ever be assessing a tiny fraction of the country's MATs.
Ofsted has been pushing the Department for Education to be able to do more to inspect the work of MATs under both chief inspector Amanda Spielman and her predecessor Sir Michael Wilshaw.
Ofsted checks on academy trusts
It is not allowed to carry out MAT inspections or give the trusts grades.
The inspectorate has developed a new MAT summary evaluation whereby it inspects groups of schools in one trust over one or two terms and then produces a summary of its findings about the MAT after the individual school inspection reports have been published.
It has carried out five evaluations of MATs so far this year and plans to do another seven before 2020.
Tes revealed yesterday that Ofsted had published a critical summary evaluation report into Bishop Anthony Educational Trust after inspecting eight of its schools.
An Ofsted spokesman said: “We select the providers inspected for MAT summary evaluations based on trying to get a broad range of academies in terms of region, size and performance.”
When asked why only 12 MATs were being looked at this year, the spokesman added: “We currently only have the resources for 12 MAT summary evaluations each year, but would be open to doing more if additional funding were available.”
Ofsted admitted last year that the majority of MATs would not be assessed through its summary evaluation system.
However, it said it was aiming to "select a broad range of MATs to visit, not just those that may be a cause for concern.
"This is to ensure that we can gain an accurate and balanced understanding of the contribution that MATs make to the school system," it added.
The most recent consolidated accounts for academies, published by the DfE last year, showed that there were 987 MATs running schools.
The other four trusts to receive a summary evaluation so far this year are Fylde Coast Academy Trust, Oxford Diocesan Schools Trust, the Active Learning Trust and Truro and Penwith Academy Trust.
Last year education secretary Damian Hinds set limits on how Ofsted should carry out its new checks on MATs.
Ofsted’s evaluation not only includes inspections of a group of schools but also survey visits to schools within the MAT – if the trust agrees – that are not being inspected.
Mr Hinds has written to Ms Spielman urging the inspectorate not to place “undue burden” on MATs when visiting these schools, and also told Ofsted not to refer to its findings as MAT inspections.
“On the school survey visits, in particular, I ask that you make clear that it is school and MAT leaders’ choice whether inspectors can visit schools that are not being inspected and to ensure that these visits do not create undue burdens on the schools or MAT," his letter says.
The inspectorate's evaluation comes in two stages. Ofsted carries out a batch inspection of schools within a trust. A regional or national director will then decide whether to go ahead with a summary evaluation of the trust, which involves discussing the report's findings with MAT leaders.