An investigation has been launched into allegations of HSC students plagiarising essays and parents bullying teachers into increasing the marks of their children at a Sydney private school.

The revelations are the latest in an unfolding plagiarism scandal across NSW, as the Board of Studies formally launches its own investigation into "endemic" cheating across the state's schools.

Pittwater House school in Sydney's northern beaches announced on Wednesday it will investigate each school department after allegations were raised over malpractice.

It is alleged that parents at the school of about 900 students have been meeting with teachers and placing pressure upon them to increase the marks of students despite evidence of plagiarism.

In one instance, parents demanded marks be altered when two students received different sets of marks after they both allegedly plagiarised an essay wholly written by the same tutor.

On another occasion a student is understood to have received a 50 per cent penalty after they stuffed notes inside their uniform, The student was only caught after they boasted about it after the HSC trial exams.

"I am treating these allegations with the utmost seriousness," said principal Nancy Hillier.

"I talk with teachers about the need to help students strive for the best - but that doesn't translate to doctoring marks or supporting students in malpractice. Should such cases come to light, it would be considered gross misconduct."

On Wednesday, teaching staff were called to submit both direct and anonymous information and a conference with faculty heads was held to launch an investigation into each department.

The inquiry at the co-ed independent school, which charges $21,600 a year, coincides with the Board of Studies formally launching its investigation into malpractice after Fairfax Media revealed that students were using a plethora of online services and private tutors to write essays for them.

"The Board of Studies can confirm that it will now focus on where students might be sourcing work which is not their own. If these activities are shown to be illegal we will take action in each case," a statement said.

According to the Board of Studies guidelines, malpractice occurs when students reproduce entire assignments that are not their own or do not acknowledge the source of parts of their work. The guidelines state that tutors are free to guide students towards important points and structure.

The concerns from teachers, parents and students at private schools echo those reverberating around the public selective school system, where Fairfax Media has revealed teachers are resigning over the level of malpractice.

Last week, the president of the NSW Teachers Federation, Maurie Mulheron, called for the end of take home assessments to combat plagiarism.