Children’s scores in English, maths and science national curriculum tests are expected to fall by up to two percentage points this summer as a result of changes to the marking system.

The dip in scores for 11 and 14-year-olds in their Key Stage 2 and 3 tests will come as a huge disappointment to borderline pupils, many more of whom will fail to reach the expected national curriculum level for their age.

Although the tests are designed to be a measure of the effectiveness of schools, they are also hugely important to pupils and their parents – and are widely used by teachers to determine which the set, or stream, in which students are placed. The drop in scores is a blow to schools that are due for Ofsted inspections in the coming year, as the results now form an important part of inspectors’ judgments.

The perception of a standstill in progress towards targets in the three Rs will embarrass the Government. The drop is predicted in a memo written by Malcolm Britton, head of statistics at the Department for Children, Schools and Families, who said it was caused by the decision this year to remove the process of “borderlining” from marking schemes. This involves remarking test papers where the original scores are just below the national curriculum level.

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