Increasing number of headteachers are leaving their jobs, a new report has found, with retention rates lowest in larger academy trusts.

The National Foundation for Educational Research (NFER) report Keeping Your Head, published today, comes as unions warn of a growing teacher recruitment and retention crisis.

Here are six key findings from the report:

1. Headteacher retention rates have fallen since 2012

The fall was greatest for secondary schools, with the retention rate dropping from 91 per cent in 2012 to 87 per cent in 2015. In primary schools, it fell from 94 per cent to 92 per cent over the same period.

The report says this is “largely attributable” to an increase in heads leaving the state education system before their retirement.

2. Headteachers are more likely to leave schools rated ‘inadequate’

The report says: “Headteacher retention rates in primary and secondary schools rated inadequate are significantly lower than schools rated good or outstanding.”

It says this is so, even after taking into account the higher levels of deprivation and lower levels of attainment “inadequate” schools tend to have, both of which are also associated with lower retention rates.

3. Headteacher retention is particularly low after a school is downgraded to ‘inadequate’…

The retention rate for headteachers of schools that drop into Ofsted’s lowest category is about 10 percentage points below the average across all secondary schools.

In contrast, when Ofsted downgrades a school to “good” or “satisfactory” (as the grade was known during the period the report examines), the headteacher retention rate is similar to that across all secondary schools.

The researchers say the trends are similar in primary schools.

4. …but if the head of an ‘inadequate’ school is relatively new, they are less likely to leave

Headteachers who are new to the post are “significantly more likely to be retained in headship” when their school is downgraded to “inadequate” than those who have been in post for two or more years.

In contrast, fewer than a quarter of heads who had been in post for at least five years when their school was downgraded to “inadequate” were still in headship - at any school - three years later.

5. Retention rates are lowest in larger multi-academy trusts

For non-academies and single academy trusts, the secondary school headteacher retention rate was 90-91 per cent, compared to 83-84 per cent in MATs with at least 16 schools.

The report says this could partly be because larger MATs tend to have high proportions of sponsored academies, which have lower retention rates on average, and partly because of more heads in large MATs moving to central roles within the trust.

But it adds: “Another hypothesis is that larger MATs are those with stronger central teams and models of school improvement, who act more quickly to remove headteachers that they identify as under-performing.”

Headteacher retention rates drop when a school becomes a sponsored academy, and heads who have been in post for a number of years are unlikely to be retained after their school converted.

6. The picture for headteacher retention in ‘challenging’ schools might not be what you expect

On the face of it, schools with lots of children from disadvantaged backgrounds, or with low attainment, have lower headteacher retention rates than non-challenging schools - 87 per cent compared to 92 per cent, in secondary schools.

However, once other differences such as Ofsted ratings and school types are taken into account, the researchers said this finding was not statistically significant.

In fact, after controlling for a school’s level of attainment, “schools with higher proportions of pupils eligible for free school meals have very slightly higher retention rates”.

The researchers conclude that pupil attainment, rather than disadvantage, drives the relationship with lower retention rates.