The annual spelling test taken by 600,000 pupils at the end of primary school found that almost all could spell "washing" and "before", while "varieties" stumped three-quarters of pupils.
Among the 11-year-olds who reached the expected level 4, less than half correctly spelt design, properties, surprising, supply, medicine, disease, available, physical, or essential.
The mistakes are revealed in analyses of last year's test papers by the Qualifications and Curriculum Authority. They also identify other howlers in English, maths and science.
In the reading test, pupils read about Bob, a cowboy who single-handedly rounded up wild horses to the amazement of other cowboys. The pupils were then asked what the other cowboys might have said to him, perhaps: "Well done Bob, you've got the horses."
The cynical pupils who wrote "Ha, ha you got the wrong horses," or "I bet you stole them," scored nothing.
In science, pupils were asked why Ian floated on water when gravity was pulling him down. They were expected to refer to upthrust, which balances gravity. But most got it wrong, with guesses ranging from: there is hardly any gravity underwater to water vapour is pulling him up or he does not want to go down.
In maths, fractions tripped up more than four-fifths of pupils at level 4 when they were asked to put them in order. The most common mistake was to order them by the denominator.
Another question showed a game using seven cards numbered 1 to 7, in which Josh scores if an even number is picked and Sapna scores if an odd number is picked. Is the game fair? Most children recognised that it was unfair because there were four odd numbers and only three even numbers, but some thought it was unfair because only one child decided the rules.