Forcing children to take Sats is a breach of their basic human rights, the general secretary of teaching union the NUT has warned.
Pupils should receive a broad education and not only be taught how to pass exams, Christine Blower told her union's annual conference.
The children's commissioner for England has to have regard for the United Nations convention on the rights of the child, which the Government signed up to in 1991, Ms Blower added.
"Some of the articles are about basic human rights," she told delegates. "These include the right to a name, the right to be safe and the right to be educated in the round, not only to pass exams.
"I think that's a pretty high authority on which to rely when we say the Sats regime is wrong and it must go."
The convention calls for education to develop a child's "personality, talents, and mental and physical abilities to their fullest potential".
Ms Blower's remarks come as members of the NUT and heads' union the NAHT are balloted for a boycott of next month's key stage 2 tests. Both unions are confident that members will vote in favour of action.
"This is industrial action with no downside," Ms Blower said. "Children will be taught, teachers will feel less stressed on behalf of themselves and those whom they teach, and parents and carers will be told how their children have done for the whole of this year across a whole range of subjects.
"Children will be praised and made to feel confident about what they can do, not made to feel a failure for what they can't."
Ms Blower quoted the children's commissioner for England, Maggie Atkinson, who questioned last month whether young people are treated as "little bundles of measurable outputs trained in a mechanistic model of education".
Mick Brookes, general secretary of the NAHT, also addressed the NUT conference earlier in the week, saying that Sats "humiliate and demean" schools with tougher intakes.
But lack of time meant that NUT members were unable to debate a motion on Sats that called for possible strike action to disrupt the future administration of the tests.
Ms Blower has been keen to stress that the proposed boycott is not a strike.
The Government has made a number of concessions on the testing regime but has so far refused to abolish key stage 2 Sats in English and maths.
Schools minister Vernon Coaker said last week: "We don't think going ahead with a boycott would be in children's best interests and we urge heads and teachers to use their professional judgment."