Pupils at the Glasgow Gaelic School took centre stage at the 13,000 capacity venue and performed Sing.
The group of 24 pupils, aged 11 to 16, discovered they would be performing with the Take That hit-maker at the end of last week after the concert promoter contacted them.
Several teachers at the school look after the choir including Mr Nicolson, Mrs McEachen and Mr Crichton, and they helped the pupils prepare for their biggest gig to date.
Gary even wished the pupils good luck before they took over his stage with their rendition of the song which you can watch below.
Kathleen MacLeod, deputy headteacher, said: "We were absolutely delighted to have the opportunity to perform at the Gary Barlow concert.
"The pupils did brilliant and we are all proud of them."