Wolfson Hillel Primary School is to start the day half an hour earlier from September in the hope that it will improve children's learning.
From the next academic year, the school day will begin at 8.20 am and end at 2.30 pm rather than start at 8.50 am and end between 3.20 and 3.40 pm (depending on the children's age).
Kirsten Jowett, headteacher of the school in Southgate, north London, said that the "primary motivation is that young children learn better earlier in the day".
She said she had been inspired by a recent visit with other teachers to Finland, which comes far higher than the UK in international rankings in children's reading and maths.
From 2.30pm, there will be an optional hour-long enrichment programme run free of charge by the school staff. While there had been a suggestion of it being led by an outside provider at a cost of GPB1 a session, after a consultation by the school this was felt to be unfair.
Lunch will be cut to 45 minutes and take the form of "family service" whereby children will serve themselves at the table rather than queue with trays.
As well as her Scandinavian trip, Ms Jowett said she had done research "on when children learn best".
The new arrangements would also help retain good teachers, she said, enabling them to develop teamwork without having to stay unduly late.
While a small proportion of parents felt the new times would be inconvenient, more than 90 per supported them, according to the consultation.
The enrichment programme would range from sports to arts, Ms Jowett said. "It could be a lego club with design and technology targets - who can build the strongest bridge. But equally it could be Maccabi netball."
To get more news, click here to sign up for our free daily newsletter.