Abercorn, in St John's Wood, is the only school to appear on the latest Electoral Commission list of people and organisations that have donated money to political parties.
The school, which charges annual fees of pound;10,000, gave three donations to the party totalling pound;15,000 between December 2002 and July last year.
Most private schools are not allowed to make donations to political parties because they are registered as charities. However, Abercorn, established in 1987, is managed as a private company.
The school places a strong emphasis on inter-house competitions and states that its older pupils are "motivated by the approbation of their peers".
Andrea Greystoke, the head, said none of the school's owners were available to comment on the donations.
Other educational organisations to fund political groups include BromCom, producers of software for recording pupil attendance and behaviour, which gave the Conservatives pound;2,500.
The Labour party received significant donations from two business figures who are sponsoring academies.
Professor Alec Reed, chairman of Reed Executive and sponsor of the West London academy in Ealing, has given a total of pound;30,000 to the party since 2001.
In the same period Labour received pound;143,000 from Sir Frank Lowe, advertising executive and sponsor of the Capital city academy in Brent However, their donations pale in comparison to the pound;1.7 million given to the Conservatives by the Institute for International Research.
Lord Irvine Laidlaw, the founder and owner of IIR, is now hoping to sponsor a series of academies in England and Scotland and has been holding talks with Newcastle city council.