Five-year-olds are being prevented from engaging in traditional play as they are under too much pressure from the national tests, teachers have warned.
Children are tested at age seven, 11 and 14
With lessons geared towards assessment, children are bored from the moment they begin formal schooling, the Association of Teachers and Lecturers warned.
Traditional play with sand and water was being replaced with work, it added.
A motion at the union's Bournemouth conference expressed concern at the loss of play in the curriculum.
A teacher at Riddlesden St Mary's Church of England Primary School in Keighley, West Yorkshire, Alison Sherratt, said children in Year 1 felt "ruled by the bell".
She said: "Pressure is now put on Year 1 teachers to prepare children for tests by removing sand, water, role-play etc and replacing with work space."
This was a "good model for how to switch children off and create failure," she said.
"In Year 1, children are already bored by constant assessment and tests. They know they're going to be tested."
Children were caught "like Frank Bruno's punch bag" between the different educational goals, she added.
Year 1 pupils were expected to cope with formal learning in a big class, and were rushing "ever closer" to testing in Year 6, she said.
A teacher at Mill Mead Community School in Hertfordshire, Jackie Harvey, said children should be given the chance to play.
But she added: "Children in my class know that play is the carrot at the end of the worksheet trail. That's not something I am happy about."
Earlier this week, ATL general secretary Mary Bousted said primary school had become a "boot camp" for 10-year-olds as teachers prepared them for tests.
At seven children in England are tested on English and maths.
At age 11 and 14 they tested again but on science as well as English and maths.