A former Hasmonean High pupil has shown his appreciation of his old school by offering a donation of up to £900,000.
But to get the full amount from the anonymous donor, the north London school will have to match it with a similar sum from other sources.
"For every £1 the school raises, the donor will give £1 up to £300,000 a year over the next three years," said Hasmonean's fundraising manager Dvora Kriss. "We are approaching other donors and we hope other alumni will follow suit."
Some of the money will help children whose families cannot afford the £2,500-plus annual voluntary contributions for Jewish studies, or the cost of educational trips. "We never turn a child away," Mrs Kriss said.
The school is also raising money for a number of projects including a room to house the successful beauty therapy vocational course for girls - currently operating out of a Portakabin - and laser-cutting machines for the design and technology courses.
"Our music room is also too small now to cope with the number of students," she said. "We have over 100 lessons a week."
Hasmonean additionally wants to start a creche for teachers. "It's very difficult for teachers to find the childcare that covers the hours they want. Staff would get first preference, but we'd open it to the community as well."
Apart from the pledge of financial support, the school has been boosted by the receipt of two awards in recognition of its educational achievements.
It has just received an Excellence in Enterprise Award from Warwick University's Centre for Education and Industry for its business programmes and an International School Award from the British Council for fostering links overseas.
"We have links with a school in Romania and we did a music concert with a school in India," Mrs Kriss added. "We are looking for sponsorship for the video-conferencing we use."