By Alison Smith
BBC News education reporter
A report into coursework by the government's qualifications watchdog said downloading essays from the internet "could not be controlled" - creating problems for schools trying to run a fair exam system.
There is going to be a review of GCSE coursework
"100% certainty that a piece of work is the pupil's own cannot be achieved unless it is written up under controlled conditions," says Daphne West, head teacher at independent girls' school The Maynard School in Exeter.
"Coursework can help stimulate interest and motivate pupils to study a subject which is of genuine interest to them," she said.
"It is important this is preserved. But it is at the writing up stage where problems can occur."
And the head teacher says that it raises questions about how much legitimate help parents and teachers should be giving to pupils.
The report highlights concern over internet plagiarism, but Ms West says that work copied from the internet is usually easy to spot.
'New generation of risks'
Nonetheless, the QCA chief executive, Ken Boston, has warned of the misuse of the internet for "deliberate malpractice".
"The availability of the internet is a powerful aid to learning but carries a new generation of risks of plagiarism."
A simple internet search under "biology GCSE essays" returns several sites where essays are available for downloading.
Many pupils were aware of such sites, the QCA report said, and some admitted trying to download essays.
Steve Sinnott, general secretary of the National Union of Teachers, said coursework was valuable as it tested a wider range of pupils' skills and abilities.
"But teachers and parents would welcome a tightening up of procedures to try to achieve consistency across the examination boards," he said.
He said firms who were "exploiting young people" by offering them ready-made coursework should be tackled. And he indicated that writing coursework up under controlled conditions would not be an unfavourable option.
Daphne West said teachers were likely to be aware of exam board guidelines in their subject, but most parents needed advice about how much help they could give.
For some subjects and boards, teachers are required to give feedback at the draft stage, but for other subjects this is not the case, Ms West said.
"At larger schools I can see where cheating with the internet could occur.
"We give talks to our Year 10 and Year 11 pupils which tell them what plagiarism is and we take the matter very seriously," she said.
"We ask exam candidates to sign a form certifying that coursework they submit is their own work."
She said that as a relatively small school with only 60 pupils in year 11, cheating was less likely to slip through the net because teachers knew their pupils very well.
The QCA also expressed concerned about "cloned coursework", where so much help was given in the form of templates, checklists and framing essays, that there was little to tell candidates' work apart.
And Daphne West agreed this was a worry: "Pupils should be demonstrating an understanding of the material they have researched.
"But they don't gain anything from cloned coursework."