EASTERN Creek Public School will lose one teacher, significantly increasing class sizes, because two pupils recently left.
Parents of the school's pupils have called on families looking for a new school to consider enrolling their children at Eastern Creek.
"It's a lovely school, friendly and welcome, like a big family," Trudi Craft, mother of three pupils, said.
The state Education Department's staffing formula stipulates a strict minimum pupils-teacher ratio at every school.
Department rules also prevent the teacher being identified and do not allow her to speak to the media.
"For a teacher that has contributed so much to face losing their job because there are 1.5 fewer kids is appalling," said Keith Darley, who has two children at the school.
"The teacher's removal will disrupt her class and push up other class sizes to about 30 kids."
Miss Craft said this would put more pressure on all children, particularly those with learning problems.
A spokesman for Education Minister Adrian Piccoli said the staffing formula had to be applied to all schools.
"It is so no favouritism is shown to a particular school," he said.
"If student numbers increase an extra teacher will be provided."
Suzanne Tatlock, mother of two pupils and a volunteer in the school's library, said the teacher's impending dismissal was "a disgrace".
"If this one teacher goes, it will affect at least half of the school," Mrs Tatlock said.
Parents have collected hundreds of signatures on a petition calling for the teacher to be retained at the school.
"We've managed to keep her employed until the end of term, so we've got five weeks to save her job," Mr Darley said.