The rumours began after teacher Christian Malone told his class of seven and eight-year-olds that the field was being sold to a company which wanted to build eight luxury homes on it.
He designed a spoof "Hampshore Homes" flyer, explaining how the project would be used to extend classrooms at Milford-on-Sea Church of England primary, renovate the toilets and provide a computer suite.
The children at the New Forest school were asked to write to headteacher Martin Pitman telling him what they thought of the scheme.
Mr Malone said: "It led to some really good work, they were really thinking and engaged. If I had said it was just pretend then you wouldn't really get their true opinions."
Mr Pitman had been told about the lesson, so that he could play along if the children approached him at playtime. At the end of the day, the class were told it had been a hoax.
"But the posters were on the wall," said Mr Malone. "The Year 6 children saw them, started talking to their parents and the village network got on to it."
"Parents were ringing up to say it was not a good idea to sell the playing field," said Mr Pitman. "There is a very close community in the village.
The gossip had already spread to the local secondary school through the pupils' brothers and sisters."
A letter was dispatched to parents, which explained that the rumour began as an exercise preparing pupils for the following week's assembly where children would be demonstrating their persuasive skills.
Mr Pitman said: "It was very realistic. We do want a computer suite."
The writing project ended with an assembly, for which the children did a spoof news report playing the parts of a reporter, demonstrators with placards, teachers and parents.