Portsmouth Grammar School held a non-school uniform day in support of the Lord Mayor’s Charity Appeal.
Councillor David Fuller, whose term as the city’s figurehead finishes next month, said he was delighted at the donation, thought to be the biggest single one made in the last 12 months.
He said: ‘I’m absolutely speechless that they have done this for us. It is fantastic.
‘I want to thank everyone who has helped us raise money. I think people need to know about the great work that has been done.’
This year’s appeal raises money for The Royal Navy and Royal Marines Charity, NHS Trust Oncology and Haematology, and Help 4 Special Children.
About £35,000 has been raised since Cllr Fuller took over.
James Priory, headmaster at Portsmouth Grammar School, said: ‘Pupils were delighted to support the three excellent local charities supported by the Lord Mayor through donating at the termly Mufti Day.
‘The amount raised reflects the commitment that the pupils have to such causes and we were all very pleased to be able to deliver such a significant donation.’