Schools across the country are braced for stike action as parents boycott the Sats exams.
Across the country tens of thousands of people signed a petition supporting a boycott in protest over exams for six- and seven-year-olds.
The Let Our Kids Be Kids campaign wants parents across England to keep their children off school today, saying they are "over-tested, over-worked and in a school system that places more importance on test results and league tables than children's happiness and joy of learning".
The petition, signed by more than 40,000 people, added: "We want our kids to be kids again and enjoy learning for learning's sake, not for Ofsted results or league table figures.
"Bring back the creativity and the fun - say goodbye to repetition and boredom."
In an open letter to Education Secretary Nicky Morgan, published on their website, the Year Two parents behind Let Our Kids Be Kids said they "represent the voice of parents across the country" who "want an end to Sats (standard assessment tests) now".
The group claims children are being asked to learn concepts that may be beyond their capability and becoming stressed and anxious.
These new Sats tests have been drawn up to assess children's grasp of the recently introduced primary school national curriculum, which is widely considered to be harder than the previous one.
Sats are taken by children aged six or seven in Year Two and then again in Year Six, aged 10 or 11, before a third set in Year Nine aged 13 or 14.
Parents are being urged by the campaign to keep their children off school for "a day of educational fun instead" and the website includes posts from hundreds of groups or parents indicating they will take part in another activity rather than attending classes.
Shadow education secretary Lucy Powell said she did not condone the action but claimed ministers had "ridden roughshod" over the concerns of headteachers and parents about Sats.
Ms Powell said a series of policy changes had caused "chaos" for schools, with 82 primary assessment documents published, updated or clarified on the Standards and Testing Agency website since the start of the academic year - an average of one every other working day.
Education Secretary, Nicky Morgan, warned that missing school even for a single day would be "harmful" and called for those behind the "damaging" campaign to reconsider their actions.
In a speech on Saturday, she said: "To those who say we should let our children be creative, imaginative, and happy - of course I agree, both as a parent and as the Education Secretary.
"But I would ask them this: how creative can a child be if they struggle to understand the words on the page in front of them? They certainly can't enjoy them.
"What are the limits placed on a child's imagination, when they cannot write down their ideas for others to read?"