Too much testing of pupils is preventing school staff from looking after children's welfare properly, the president of Britain's largest teachers' union has warned.
Lesley Auger told the National Union of Teachers (NUT) conference in Harrogate, North Yorkshire, that exams at age seven, 11 and 14 were "stifling" creative development and forcing schools into competition with one another.
The union is due to vote on whether to call for the abolition of compulsory tests - in English, maths and science - on Sunday.
Ms Auger told delegates: "A friend of mine, a teacher of five year olds, was met by a tearful child one morning. The child's grandfather had died the previous day.
"The child was inconsolable and the rest of the class wanted to know what was happening. It was soon clear that many of them had a similar story to tell.
"My friend looked at the targets for the first lesson lying on her desk: should she abandon the lesson and discuss this important event with the children?
"She did, but she was later mortified that she had even contemplated continuing with the lesson."
Ms Auger said this was "symptomatic" of the pressures to achieve testing targets.
The NUT says organisations such as Childline are increasingly receiving phone calls from children affected by exam pressures.
Ms Auger said: "These consequences of a testing regime are ignored at our peril.
"We are forced to acknowledge them as long as league tables pit school against school, as long as parents are able to shop around for so-called "best schools", and as long as teachers are compelled to accept performance management targets based on the measurable performance of children."
The government has set a target of 85% of 11 year olds reaching the required standard in English and maths by 2004.
Last year, 75% did so in English and 73% in mathematics.
The National Association of Head Teachers has warned the target is unlikely to be reached.