HUNDREDS of thousands of last-minute and "pirate" exam entries are clogging up the system and could delay results.
The Government's exam watchdog, the Qualifications and Curriculum Authority, has warned that exam boards cannot guarantee to deliver grades to schedule unless they receive details of late entries and coursework marks urgently.
Examiners are also bracing themselves for "pirate" entries - candidates of whom they are unaware until their scripts turn up.
Last-minute exam entries have become an increasing problem. Last year, around 1.5 million entries were sent in after the deadline - about one-fifth of the total. A stream has continued to arrive after this year's March deadline.
So called "pirate" entries are particularly difficult to resolve. A student sits the paper and the script is marked, but the school does not notify the board so the candidate is never officially entered. The confusion generates mountains of paperwork in a system that is overwhelmingly computerised.
Students also change their options at the last minute. For example, in maths, a significant proportion of pupils switch from the intermediate tier to the higher tier or vice versa.
George Turnbull, head of public relations at the Assessment and Qualifications Authority, said: "It may seem like a minor inconvenience, but tracing candidates can take a huge amount of time."
Jerry Jarvis, director of operations at Edexcel, said: "Late entries may be a small proportion of what we deal with but it is still significant numbers of students which creates considerable pressure.
"If 1,000 students appear out of nowhere at the end of July, it is very difficult to deal with, no matter how good planning has been. In a subject where examiners may be in short supply, such as psychology, it can be a real struggle."
Mr Jarvis said his greatest concern this season was schools and colleges failing to return coursework scores. "Not getting the marks through is like a candidate missing an exam," he said.
Bill Kelly, the QCA's head of quality, has issued a warning to schools. "If marks are not received on time, the awarding bodies are unable to guarantee results on the due date. For the sake of the students, that is a position that we would all rather not reach," he said.
But schools have complained that timescales are too tight. For instance, there was only two weeks' grace between the notification of grades achieved in the January modules and the deadline for entering pupils for a summer re-sit.
John Dunford, general secretary of the Secondary Heads Association, who earlier this year said the exam system was heading for a Railtrack-style meltdown, said: "These problems are indicative of how over-complex the exam system has become.
"It illustrates that the complexity causes as many problems for the exam boards as it does for schools.
"The weakest part of the Government's recent 14-19 Green Paper was its failure to address this problem."