Jeremy Corbyn has announced plans to abolish primary school Sats.
Speaking at the National Education Union's Conference in Liverpool, the Labour leader set out proposals to scrap the "regime of extreme pressure testing".
Labour said the policy would relieve pressure on a schools system forced to cope with overcrowded classrooms, and an ongoing crisis in teacher recruitment and retention.
Mr Corbyn said: "We need to prepare children for life, not just for exams.
"Sats and the regime of extreme pressure testing are giving young children nightmares and leaving them in floods of tears.
"I meet teachers of all ages and backgrounds who are totally overworked and overstressed. These are dedicated public servants. It's just wrong."
Mr Corbyn also announced that the next Labour government will scrap baseline assessments for reception classes.
He said Labour would consult parents and teachers on an alternative that "prepares children for life, not just for exams".
Labour’s schools minister defended the proposals to get rid of the tests, saying that English children are “some of the most tested in the world”
Mike Kane told talkRADIO’s John Nicolson: “The tests don’t add value to the children’s education. They simply narrow the curriculum and England has now got a reputation of teaching to tests.
“We need a balanced and broad curriculum and remove the stress from these tests from our youngest students.”
He added: “English school children are some of the most tested in the world.
“There is increasing evidence that children are losing sleep because they are stressed. They are developing school-phobias because of these two key tests.”
Mr Kane suggested that parents would “hugely welcome” the abolishing of Sats.
However, Schools Minister Nick Gibb condemned Mr Corbyn's plan to end Sats.
He said: "These tests have been part of school life since the 90s. They have been pivotal in raising standards in our primary schools.
"That's why Labour governments led by Tony Blair and Gordon Brown supported them.
"Abolishing these tests would be a terrible, retrograde step. It would enormously damage our education system, and undo decades of improvement in children's reading and maths.
"Labour plan to keep parents in the dark. They will prevent parents from knowing how good their child's school is at teaching maths, reading and writing.