The ending of science Sats has led to the primary curriculum being even more skewed towards English and maths, headteachers and teachers' leaders warned this week after a dramatic drop in science scores.
The proportion of children reaching level 4 in science dropped to 81 per cent from 88 per cent last year after sample tests were brought in to measure national performance. Just 28 per cent of pupils taking sample tests reached level 5, compared with 43 per cent last year.
Sample tests are not used to hold schools accountable, so the difference could be due to "teaching to the test" in previous years, rather than a genuine fall in standards.
The NUT warned that the focus has shifted from science because of the high stakes in the core subjects.
The union's head of education John Bangs said: "The issue is that science has been a major success story for primary schools. The focus now on English and maths has taken that focus off science. That is the nature of high-stakes testing; to focus on English and maths and not on everything else."
Sion Humphreys, assistant secretary of heads' union the NAHT, said: "It all boils down to the fact tests are still associated with a regime of high-stakes testing - it could be that because science has been removed, more time and effort has gone into English and maths."
The sample science tests were carried out in 747 schools; individual results were not returned to pupils, schools or local authorities. Heads warn that less effort may have gone into science this year, as schools are still held accountable for English and maths results.
Alison Peacock, head of Wroxham Primary, Hertfordshire, ran the sample tests in her school, boycotting English and maths Sats. She echoed the view that the drop in results may be because of a "basics versus the rest" mentality that put pressure on teachers.
"Has science joined the long list of subjects narrowed in pursuit of the English and maths scores so highly prized for Ofsted accountability purposes?" she said.
She added: "I fear that these results are going to be used against the profession and that's a great shame."
John Gawthorpe, head of Mayhill Junior, Hampshire, also used sample tests.
He said his school had used its science time on broader science learning and teaching.
He added: "Whether we did as well as previous years in the science tests, maybe not, but I shan't lose a wink of sleep over that. This year Year 6 did more science learning and less science revision."
Marianne Cutler, director of curriculum innovation at the Association for Science Education, said the sample tests had not yet caught up with the broader curriculum that dropping national testing allowed.
She said: "If more effort is going on English and maths, where schools are accountable, that is worrying. I don't want Sats back - personally, I think it's far too early."
Teacher assessment, carried out in all schools, revealed a drop to 85 per cent reaching level 4, from 86 per cent in 2009.
- Original headline: Unions blame KS2 science stats on English and maths Sats