More than 750 kids from Baden-Powell and St Peter's Church of England Junior School in Poole, Dorset, were packed into church for a Christmas service when their teachers suddenly started to burst into song.
Head teacher Paul Howieson kicked things off by reading the first verse aloud before breaking into song.
Then groups of teachers popped up from seats around the church to join in - and even the rector, Reverend Michael Camp, had a part in the performance.
Mr Howieson told the local paper: "We have been working on the performance for the last three weeks and did two or three rehearsals in the church and several at school.
"We had to close the curtains and pretend nothing was going on but it worked. I don't think anybody had any idea what we were up to.
"I read the first verse and the kids started to stir by the third word and by the time I got to the line 'looks like I'm the queen' they were laughing. Their reaction was extraordinary.
"I think it's good for them to see their teachers in a different way, and see we like a laugh as much as anyone. And it was great to get Revd Michael involved too. It's a really positive association with the church for the kids.
"We're a big school so getting everyone together for a rehearsal was not very easy but we did it and we managed to keep it a secret.
"All the parents said how great they thought it was. The problem now is finding a way to go even bigger next year and keep it a secret."
Let It Go is the main song from Disney's Frozen, the most successful animated film ever made.
It is sung by Queen Elsa, voiced by Idina Menzel.
Watch the performance in the video below