Thousands of children at level 4 struggled with everyday words such as "destination", "headquarters" and "strength". The most difficult word was "physically", which 15 per cent of level 4 children and 62 per cent of the more-able level 5 children spelled correctly.
But the tests revealed that 11-year-olds are better at using some punctuation than 14-year-olds.
A third of 11-year-olds used speech marks accurately in the writing test but only one-fifth of teenagers managed it.
On average, secondary school pupils spelled just over 96 per cent of their words correctly. However, common words were misspelled, even by pupils achieving above their age.
In maths, 11-year-olds had difficulty with decimal points.
The reports from the Qualifications and Curriculum Authority detail how pupils performed in the 2002 national tests.