Teachers and school leaders will know the significance of 190 days - the number of days that schools are typically open for over the course of an academic year.

While this is only a statutory requirement for local authority maintained schools, the freedom that academies and free schools have for more flexible term times does not seem to have been widely used.

There is, however, no legal minimum for how long any school should be open for in any given week. So in 2022 the previous government laid out the expectation that from this academic year, state-funded mainstream schools should deliver a school week of at least 32.5 hours.

At the time the government accepted that the majority of schools were already offering this minimum, and this was confirmed in surveys of schools.

The effect of longer school days

As part of its system for monitoring adherence to this new minimum, the Department for Education started requiring all schools to return their weekly opening hours as part of the School Census.

At the Education Policy Institute, we have taken a look at what this new data collection tells us about the length of the school week and its potential impact on pupil outcomes.

We found that in 2023-24 four in five primary schools and three in four secondary schools had school weeks that were at least 32.5 hours long.

So, while previous analysis was right in showing that most schools were already meeting the minimum-hours threshold, there are still plenty of settings where the new requirement would mean increasing time in school - though typically not by much.

These differences in weekly hours across schools can appear small, but they do, of course, add up - an extra hour a week of school is equivalent to more than a week of school over the course of a year.

The question is, does that additional time matter?

More on longer school days:

• Do longer school days work? Lessons from history
• Extending the school day ‘could cut absence’
• Why we should extend the school day

The EPI previously carried out research into this question for our report An Evidence Review into the Length of the School Day, published earlier this year.

In our latest analysis were able to link the data on the length of the school week with pupil attainment data at key stage 2 and KS4 and examine the relationship between the length of the school week and pupil outcomes in England for the first time.

We found that additional time in school was associated with a small, yet positive, effect on overall attainment at the end of both primary and secondary school.

An additional hour of secondary school time each week is associated with a 0.17 grade improvement in one GCSE subject.

Meanwhile, an additional hour of school each week in primary is associated with improvements in KS2 scaled scores of 0.053 and 0.066 for maths and reading, respectively.

This is consistent with existing international evidence that points towards additional time in school having modest effects on overall attainment, in both country-specific and cross-country studies.

If we put these effects at primary and secondary on a comparable scale the impact of an additional hour each week at primary is higher than secondary (0.020 compared to 0.018 standard deviations), again consistent with international evidence.

At first glance, the effects would appear to be quite small, but there are some important caveats.

The current data collection requires schools to only report the total time pupils spend in school each week, so we are still none the wiser about what the make-up of the school day is: how much time is spent learning rather than on lunch or breaks? And in that learning time, how much time is spent on each subject and how broad is the subject mix?

We should perhaps not be surprised, therefore, if results are a bit mixed.

The challenge for all schools, but particularly for those faced with increasing the length of their school week, is how time is used.

The right mix of activities

In previous studies, additional hours have been found to have a greater effect on test scores when pupils are instructed by the same teachers who conduct their regular classes, emphasising the importance not just of specific training and experience but also of fostering a well-established connection between students and teachers.

We also know that additional time is more likely to have a significant and positive impact on pupil academic outcomes when conducted in a one-on-one setting or in very small groups of two to three participants and a teacher. However, there are clear cost barriers to implementing this at scale.

Given the constraints (cost and otherwise) on increasing time in school, it is important to better understand which mix of activities during the school day deliver the best outcomes for pupils.

Louis Hodge is associate director for school system and performance at the Education Policy Institute (EPI)