Jeremy Corbyn has pledged that Labour would scrap formal tests in primary schools in England, known as Sats.
The tests left children in floods of tears or vomiting with worry, he told members of the National Education Union in Liverpool to loud whoops and cheers.
He said it would free up schools struggling with funding cuts and congested classrooms, and help teacher recruitment and retention.
The move means school league tables based on the tests would be ended too.
"We need to prepare children for life, not just exams," he said to a hall of cheering teachers
Members of the teaching union have called for primary school tests to be ditched for many years and gave the Labour leader a standing ovation.
They have long argued that the high-stakes nature of the tests skews children's education, and turns primary schools into exam factories.
Mr Corbyn told members the next Labour government would end the Sats all pupils have to sit at seven and 11, the results of which are used to hold schools to account.
Instead, Labour would introduce alternative assessments which would be based on "the clear principle of understanding the learning needs of every child."
The government has already said it is phasing out Sats for pupils aged seven, and instead it wants to bring in a new baseline assessment for reception classes.
Reacting to the announcement, joint general secretary of the NEU, Dr Mary Bousted, said Mr Corbyn recognised the damage a test-driven system does to children and schools.
"We look forward to the return of a broad and balanced curriculum and to the rekindling of the spirit of creativity in our schools."
Head teachers' leaders also welcomed Labour's announcement.
Paul Whiteman, leader of the National Association of Head Teachers, said children's progress could be measured through "everyday teacher assessment and classroom tests", while Julie McCulloch, director of policy at the Association of School and College Leaders called Sats "flawed", with a new approach "long overdue".
Schools Minister Nick Gibb said abolishing Sats "would be a terrible retrograde step" which would "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," said Mr Gibb.
But Mr Whiteman said Sats do not tell teachers or parents anything they do not already know about their child.