The government must give up its "continuing obsession" with testing England's schoolchildren, a head teachers' leader has said.
Ministers say testing is essential
Desmond Hamilton, president of the National Association of Head Teachers, also demanded that no class should exceed 30 pupils in size.
Personalised teaching - not "tests for tots" - was needed, he told the NAHT's annual conference in Harrogate.
Ministers say tests are essential for raising standards.
'Invisible and intangible'
Dr Hamilton told conference delegates: "There are no mistakes in schools, only lessons to be learnt.
"We are knowledge creators. What we do often remains invisible and intangible.
"Yet government has a continuing obsession with leaving no person under-tested.
"Those for whom classroom visits are occasional photo opportunities often reflect most enthusiasm for testing regimes - not classroom teachers."
Dr Hamilton's call for smaller class sizes comes after government figures showed the number of five to seven-year-olds taught in groups of more than 30 pupils - the legal limit - had risen from 740 to 910 in a year.
Schools must seek permission for form groups to go "oversized".
Dr Hamilton suggested the best way to organise classes would be to multiply a child's age by two, so a five-year-old would be in a class of 10 pupils.
The NAHT conference is also expected to hear calls to end the practice of school inspectors sending letters about their findings to pupils.
A motion for debate states: "At best, these letters are patronising, condescending and supercilious.
"At worst, the letters may expose and humiliate some teachers.
"The practice flies in the face of the 'respect agenda' by giving children licence for bad behaviour."
The conference is on until Monday.