Parents supporting the Let Our Kids Be Kids campaign have kept children out of school.
More than 40,000 parents have signed a petition calling for primary school tests, which are due to be taken later this month, to be scrapped.
The number of children kept at home today (3 May) is still unsure.
A social media campaign has been urging parents to take children on educational activities for the day.
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."
New data from the Youth Sport Trust’s annual Girls Active Survey has found that girls with multiple characteristics of inequality are being left behind in PE and school sport.
Nearly three-quarters of teachers (72%) say the current SEND system fails children, yet more than half (56%) expect anticipated reforms to negatively impact SEND pupils with complex needs.
Over a quarter of all schools and colleges across England are taking part in the free National Education Nature Park programme, which sees young people create nature-rich spaces on school sites.