Numbers of parents have kept their children off school for the day in a protest about primary tests in England.
More than 40,000 parents have signed a petition calling for a boycott of primary school tests, which are due to be taken later this month.
Parents supporting the Let Our Kids Be Kids campaign have complained of a damaging culture of over-testing.
Education Secretary Nicky Morgan says taking pupils out of school "even for a day is harmful to their education".
It remains uncertain how many primary school children were kept off school across the country, but a social media campaign had urged parents to take children on educational activities for the day.
About 500 people gathered at Preston Park in Brighton, including children's laureate Chris Riddell.
"We should be turning children into readers with the pleasure that gives, rather than relying on a testing culture," said Mr Riddell.
Parents have handed in the petition at the headquarters of the Department for Education in London. Among the parents present was Caterina, with son and daughter in Ivydale school in Nunhead, south London.
The campaign organisers say children 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".
They have raised concerns about the impact of primary tests, so-called Sats tests, taken by seven-year-olds and 11-year-olds, which are being made more stretching with changes to the curriculum.
They have challenged what they claim is a "dull, dry curriculum" based around tests.
In an open letter to the education secretary, campaigners have warned of schools becoming "exam factories" and that testing causes stress and can make young children feel like "failures".
Ofsted chief Sir Michael Wilshaw rejected these arguments, saying that improving social mobility depended on making sure that children are not falling behind at any early age.
"The government is right to introduce greater structure and rigour into the assessment process. Those who oppose this testing need to consider England's mediocre position in the OECD education rankings," said Sir Michael.
"As I have long argued, children who fall behind in the early years of their education struggle to catch up in later years."
Education Minister Nick Gibb said tests improved standards and need not be stressful.
"Schools should not be putting pressure on young people when taking these assessments.
"I've been to many schools where the children don't even know they're taking the tests," said Mr Gibb.
The importance of testing was emphasised by Chris McGovern, chairman of the Campaign for Real Education.
He said that any short-term stress was worth it if in the longer term it meant that children finished school with better results.
Schools minister Nick Gibb was asked a question on BBC Radio 4's World at One from a grammar test for 11 year olds
Martha Kearney: Let me give you this sentence: "I went to the cinema, after I'd eaten my dinner." Is the word "after" there being used as a subordinating conjunction or a preposition?
Nick Gibb: Well it's a preposition.
Martha Kearney: I don't think it is.
Nick Gibb: "After" is a preposition. It can be used in some contexts as a word that coordinates a sub-clause, but this isn't about me.
Martha Kearney: But I think in this sentence it's being used as a subordinating conjunction.
Nick Gibb: Fine, well this isn't about me, this is about ensuring that future generations of children - unlike me incidentally, who was not taught grammar at primary school...
Martha Kearney: Perhaps not.
Nick Gibb: ...We need to make sure that future generations of children are taught grammar properly."
Mr McGovern said that tests in England's schools needed to be tougher to catch up with international competitors.
"We're three years behind the Chinese at the age of 15. We are a bit of a basket case internationally.
"We've got to do something, we've got to act early, and a health check at seven is a good idea."
Ministers have already had problems with the administration of primary school tests this year.
The baseline tests, which were intended to be a benchmark for measuring progress, were found to have unreliable results and have been postponed.
Tests for seven-year-olds in spelling, punctuation and grammar also had to be called off when it was found that test questions had mistakenly been published on a Department for Education website.
Labour's shadow education secretary Lucy Powell said she did not "condone children being taken out of school".
But she accused the government of "creating chaos and confusion in primary assessment".
Russell Hobby, leader of the National Association of Head Teachers, said: "I think the gap between the profession and the government has never been wider than it is at the moment."
He warned of "an enormous number of mistakes, delays and confusions around testing".
But Education Secretary Nicky Morgan has argued that raising standards will improve creativity and not restrict it.
"How creative can a child be if they struggle to understand the words on the page in front of them?" Mrs Morgan told head teachers at the weekend.
"That is why the campaign led by some of those who do not think we should set high expectations, who want to keep their children home for a day is so damaging.
"Keeping children home, even for a day is harmful to their education."