There are serious concerns about the reliability of this year's English tests taken by 14 year olds in England. This year, reading and writing parts of the national curriculum tests were sent to different examiners, as part of an electronic marking trial. There was a delay in sending out the results to thousands of students, with some arriving after term ended. The National Assessment Agency has apologised, but head teachers fear there may be a bigger problem. Combining the results took longer than predicted, so that even an extended deadline was missed. The problem primarily affected the Key Stage 3 national curriculum English tests - those taken by students aged 13 and 14, in their third year of secondary school. In electronic or "e-marking", paper scripts are scanned into digital form so they can be divided up and sent electronically to markers who specialise in different areas - in this case, the reading and writing parts of the tests. The marking was done by the AQA exam board. The results were collated by the Data Collection Agency, part of the Pearson group. A spokesman for the National Assessment Agency said: "The Key stage 3 English marking process was changed this year to improve marking quality. "Markers opted to mark either the reading or the writing papers. "The marking period was extended by a week to allow time to marry up the reading and writing marks and calculate an overall level for English. "However, for some schools the process took longer than expected. "We recognise that for some schools this made it difficult to report results to parents by the end of term, and we have apologised for the inconvenience this delay has caused." Not only that, but it appears wrong marks were sent out to some schools. Derbyshire teacher Gill Chesney-Green told BBC News Online: "The English Sats results in our school have been examined carefully - and there are a lot of mistakes in the addition of marks." Many of the scripts were being returned, delaying the results for the school. "Apparently this is happening on a large scale locally," she added.