Ministers are facing renewed pressure to scrap Sats tests as new figures showed the number of pupils reaching the required standard in English has fallen for the first time in the history of the exams.
A fifth of primary school pupils, around 115,000 in total, failed to reach Level 4 in the subject, according to results published by the Department for Children, Schools and Families (DCSF).
This is down one per cent on last year, from 81 per cent to 80 per cent, and the first time there has been a drop since 1995.
Teaching unions warned they had concerns about the quality of marking, particularly in writing tests.
Opposition ministers said the results showed progress in maths and science had stalled while English standards are now slipping.
More than a fifth of pupils (21 per cent), around 121,000, failed to reach Level 4 in maths, the same proportion as last year, while one in eight (12%), missed the level in science, again the same as last year.
Pupils who do not reach Level 4 in English are not able to read between the lines of a story or understand the moral, or message behind it.
They also struggle to write extended sentences using punctuation such as commas.
Children who do not reach Level 4 in maths do not know all their times tables - up to 10 x 10 - and cannot plot co-ordinates on a graph or work out area and perimeter. The figures also showed almost two fifths of 11-year-olds are still failing to grasp the finer points of the three Rs.
Just 61 per cent reached Level 4 in reading, writing and maths - down one per cent on last year.
Almost three in 10 (28 per cent) failed to reach this standard in English and maths overall. This was also down one per cent on last year.
A child’s reading and writing scores are combined to give an overall English result.
The Government has a target for 78 per cent of children to reach Level 4 in English and maths by 2011.
Schools Minister Diana Johnson said meeting that target would be “challenging” and added she was “disappointed” with the drop in English results. She said it was “not possible” for the Government to say that 100 per cent of children should be reaching Level 4 as many of those who do not reach this standard have learning difficulties or speak English as an additional language.
The figures revealed boys are still lagging behind girls - particularly in writing.
Four in 10 boys failed to reach Level 4 in their writing test compared with a quarter of girls. In reading, almost a fifth (18 per cent) of boys did not reach the required standard, against one in 10 of girls.
In English overall, a quarter of boys did not attain Level 4, compared with 15 per cent of girls. Ms Johnson said one of the Government’s main concerns was boys falling behind in writing, adding that new schemes have been introduced to encourage boys to write from an earlier age.