By Katherine Sellgren
BBC News education reporter in Bournemouth
Pupils have been reduced to widgets on a production line by the high number of tests in England's schools, head teachers have warned.
Head teachers say tests can lead to the humiliation of pupils
The National Association of Head Teachers said tests contributed to poor attendance and led to an exodus of young people from school.
The NAHT said, while it believed in testing, the current regime was rigid and in need of an overhaul.
The government said tests were part of its drive to raise standards.
It said the way results were published in annual league tables resulted in the "ritual humiliation" of children, their teachers and communities.
The union has now launched its own inquiry into the effects of testing and league tables.
Speaking at the start of the NAHT's annual conference in Bournemouth this weekend, general secretary Mick Brookes said it was "high time" for those in power to heed the message.
"The weight of evidence against the current system is growing.
"We would like to work with the government to map a more meaningful assessment system that avoids the dangers so clearly outlined by the NAHT and others."
Dr Rona Tutt, who is chairing the NAHT inquiry, said many people were concerned about the number of tests pupils in England were expected to sit.
"England is becoming very isolated in being the only country that feels the need to operate in this way" she said.
Sue Palmer, a former primary head teacher and author of Toxic Childhood, told the NAHT inquiry that children had been reduced to widgets.
"Each five-year plan is geared to ensuring schools provide more widgets than the previous plan.
"That's what we've been reduced to and I find it utterly tragic.
"It leads to coaching and boosting - the boredom levels are huge.
"Even the brightest kids ask teachers 'Is this a test?' and if it isn't they switch off."
The Department for Education and Skills said tests were necessary and "here to stay".
A spokeswoman said: "They provide valuable objective evidence in the core subjects, helping inform further improvements to teaching and learning.
"This is an important part of our drive to raise standards in the basics even further in primary schools.
"They are not designed to be 'pass or fail' examinations and we have stressed that preparation time should be kept to an absolute minimum and that teachers help children prepare best when they teach the core subjects as fully and effectively as possible."