Putney Park School is to close at the end of the academic after its owners told parents they have decided to sell up.
The decision means all staff will be made redundant in July and more than 100 pupils will have to find a new school at a key stage of their academic life.
Parents were sent an email out of the blue this week which partly explained the situation, citing a projected low intake for the next academic year.
The email read: "This decision has not been taken lightly. In view of this year’s low intake and the projections for September 2013 entry, it is with sadness that it is not possible to maintain a financially viable school beyond the end of this academic year.
"We are therefore proposing for the school to close on July 4."
The school, based in Woodborough Road, is celebrating its 60th anniversary this year and caters for girls aged 5-18.
Head of the Upper School Jan Black said the move would be an "absolute nightmare for parents and for the pupils".
The school's board have said they are "extremely disappointed".
A disgruntled parent, Ian Moody contacted the Wandsworth Guardian and said: "Brian Tweedie-Smith (the current head) has decided to sell Putney Park School to developers despite other people wanting to keep and run a school and willing to buy it off him.
"It goes to show that he is only interested in getting as much as he can when he is letting down groups of young children, who are half-way through their education, when the schools closes on the July 4."
A group of distraught year nine students said they were "devastated" about the news.
They said: "Our school is being forced to close despite the teachers and children all wanting it to stay.
"It is a really special school as it is very small and nurturing for children who need more help or gain in confidence.
"We are all struggling to find the right place to get the right education.
"Year 10, especially, are finding it all very tricky as they are half through their GCSEs.
"So everyone is devastated about the sudden closure of the perfect school. SOS Save Our School."
The school was founded by Mr Tweedie-Smith's aunt Jean in 1953 - the new school's philosophy was "to bring out the best in every child" by providing "safe, stable and stimulating surroundings".
Its buildings, which have housed the school since 1956, consist of four Edwardian houses.
The buildings, which are believed to be worth in excess of £6m, are situated within more than an acre of landscaped gardens.
Are you a parent, teacher or pupil at the school? Email your views to jhenderson@london.newsquest.co.uk. Alternatively contact the news desk on 020 8722 6343.
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