A section of the key stage 1 spelling paper, "A butterfly is born", required children to spell thread, stretch, wriggles, early and crumpled.
None of these spellings appear in the list of about 200 high-frequency words that children are supposed to learn during their first years at primary school.
The test is marked by awarding one point for getting the first three letters right and two points for spelling the whole word correctly.
Key stage 1 teachers and heads said the use of words such as "thread" and "wriggles", where the first part of the word is not spelt phonetically, meant children would lose out on at least one point. Elizabeth Wilson, head of Coleford primary school in Hull, said the tests were "incredibly difficult".
"It will certainly affect the results."
Judith Cooper, KS1 teacher from Taylor Road primary, Leicester, said:
"Hardly any of the words were common. Only very experienced readers had a chance of getting some of them. They were more like the kind of words you would test 11-year-olds on. Using a science topic to check spelling was a goodidea because it was cross-curricular but I think a lot of children will miss out on achieving level 2."
Primary curriculum expert Sue Palmer said: "Teachers have said they thought the spelling test was particularly hard this year and I agree."
Seven-year-olds have shown a marked improvement in spelling over the past four years.
A Qualifications and Curriculum Authority spokesman said the words in this year's KS1 test were no more difficult than in last year's test. He said children were expected to spell more words than just those on the literacy strategy's high-frequency word lists.
However, large numbers of children starting secondary school still have problems with everyday words such as necessary and environment.
KS1 spelling test: For some children, particularly those who were just level 2, they weren't going to get it.
The spelling test for 11-year-olds this year included: themselves, surprise, perfectly and individual.
KS1 spelling Test
Boy, log, sunshine, leaf, cloud, beetle, stone, grass, smiling, children, worm, lay, early, taste, discover, feeding, month, fully, hangs, thread, colour, all, stretch, bigger, wriggles, this, forms, few, breaks, unfolds, crumpled, waits