Lengthening the school day by 30 minutes would cost £2.7bn a year and there is 'insufficient evidence' it would improve results, a report has said today.

Education charity Impetus analysed the length of the school day across a random sample of schools across England. It found there is little correlation between classroom hours and pupil attainment, with great variation in outcomes between schools that have the same length of day.

It did find the length of the school day did have a bigger impact at Key Stage 4, but there was still variation between schools with different lengths of school day.

The charity is calling on the Department for Education to prioritise spending on proven interventions that will benefit the most disadvantaged pupils.

Eleanor Harrison, CEO of Impetus, said: 'Catch up funding is vital and should be spent on evidence-based interventions. While an extension of the school day may make policy sense in terms of offering more contact time, extra-curricular activities or improving wellbeing - it should not be hailed as the silver bullet for education catch up.

'In order to best serve pupils, the Department for Education must prioritise spending the catch up budget on proven interventions that will benefit the most disadvantaged pupils, and invest more in gathering data to better inform policy making.'

The charity is calling on the Government to focus on evidence-based, targeted interventions. This includes spending £848m to provide the most disadvantaged students with 12 hours of small group tuition, and £55m to put oracy support in all schools.