Schools fear not being able to challenge grades of exam papers assessed by computer. Examiners using an on-screen marking system are grading essays without giving schools and colleges any indication of why pupils are being allocated particular marks.
The TES has been shown a copy of an English language and literature AS paper in which the candidate has written more than five pages on one question, yet there are no comments or ticks by the examiner. The only feedback is the total number of marks: 30 out of 50.
The paper contrasts with a conventionally marked one completed by the same student, which is peppered with ticks and comments.
Bedford Modern School, an independent secondary in Bedfordshire, said it also received scripts in A-level music technology, chemistry, Government and politics, English literature and physical education without any annotations.
All were marked under Edexcel's on-screen system, in which scripts are scanned and sent to markers to examine at the computer.
Bedford Modern is now questioning how it can challenge the grades and how senior examiners can ascertain that the marker is working to the mark scheme.
Stephen Smith, headmaster, said: "Usually you can see where the examiner has allocated marks. When you want to query marks, you need to see the examiner's thinking.
"If you look at a paper and it has no comments or ticks on it, you don't know where the marks have been awarded.
"What you are forced to do is look at the whole paper and make your own judgment. It makes it harder to challenge marks. It makes you wonder why (the exam board) is wanting to go down this line."
In September, Tolworth Girls' School in Surbiton, Surrey, complained that A-level history scripts marked under Edexcel's ePen system had been sent back without comments.
This year, around 90 per cent of Edexcel's scripts were marked in this way. The board said its technology allowed examiners to make comments, but would not confirm that this was a requirement.
Margaret Tomkins, who stood down as an Edexcel examiner this year over on- screen marking, said examiners did not annotate using the system because it was cumbersome and time-consuming.
Edexcel's new Results Plus service offers schools a detailed statistical breakdown, it said.
A spokeswoman said: "Results Plus data provides far more evidence on student performance than ad hoc annotations, and access to the right part of the mark scheme."
The absence of annotation is less of an issue for England's other two boards as they have yet to allow on-screen marking of long essays.
A spokeswoman for the AQA board said: "We are still researching whether essay-style questions can be marked effectively on screen. If we did start marking such longer answers electronically, we would certainly expect our instructions to require examiners to annotate."