Anita Straker, head of the Government's maths strategy, says that the practice is damaging and OFSTED's evidence is "flimsy and inconclusive". The trend means children as young as five are at risk of being labelled failures, she told teachers last week. Some schools changed their classes simply to find favour with inspectors, she claimed.
A recent OFSTED report, Setting in Primary Schools, pointed to "spectacular" improvements and said the practice should be considered by all primaries. But an analysis of 20 research studies in the UK and the United States, compiled by the National Foundation for Educational Research, found that setting had no overall impact on pupil achievement.
"Who's to say it's the setting that makes standards go up?" asked Ms Straker, referring to OFSTED's report. "Half the schools have taken on another teacher. Maybe it's the smaller class size, not setting. Maybe it's the fact that everybody's focusing on maths.
"I don't think it's nearly as clear cut as this report would have you believe. From what I can find out, the research evidence is very flimsy and inconclusive.
"This (move to setting) seems to come from schools who want to do it on the basis of this is what Ofsted inspectors want to see."
The most worrying development was the increase in setting from Year 1, leading to children being labelled bottom set from age five - something she believes is unlikely to leave them with a positive attitude towards maths later.
Ms Straker, speaking at the Association of Teachers of Mathematics' joint conference with the Mathematical Association, also warned of problems emerging in the way teachers are interpreting the numeracy strategy.
For example, in mental calculations, teachers are spending too much time on dealing with "special cases" - such as adding doubles, or adding near doubles - instead of focusing on general strategies applicable in most cases. Learning to do sums in their head does not mean children cannot write anything down - personal or informal jottings can help develop and reinforce quicker strategies, as can extended layouts in written calculations.
She also challenged the classroom convention that written strategies should build on those used for mental calculations when they are difficult to relate to each other.