Head teachers cannot and will not endure another year of the "chaos" that has raged in England's primary schools, a union leader has said.
Russell Hobby closed the National Association of Head Teachers' conference by calling for a fundamental review of assessment of pupils.
Pupils should only be formally assessed at the start and end of primary school, he said.
A government spokesman said it was committed to measuring pupil progress.
Reception tests were due to be introduced last month but the plans were axed.
The government had approved three separate baseline tests, which were to be used to measure the progress of pupils from when they start primary school to when they leave at age 11.
Thousands of schools had adopted one of the three, only to be told they were not going to be used to measure progress as had been intended.
Ministers say they are committed to a new baseline test and are working on new plans for this.
Teachers have also been grappling with a new curriculum, new tests and assessments, and complained of a lack of information.
Heads expressed their anger with the situation on Saturday when they heckled and jeered Education Secretary Nicky Morgan.
Mr Hobby told delegates in Birmingham: "We cannot and will not endure another year of chaos.
"School leaders cannot do their duty to children under these circumstances."
He also called for a new approach to assessment of pupil's progress in primary schools.
Currently pupils are assessed formally through national tests at age seven and 11.
He said: "If you are going to measure progress you need a start measure and an end measure.
"And you should start at the beginning of school, not in the middle, missing out the most important years of a child's education."
But any Reception baseline test would have to be "one that works" and "not the mess that we've seen this year", he said.
He argued that statutory assessments for Year 2 pupils should be scrapped: "We cannot have two high-stake tests for young children."
A spokesman for the Department for Education said: "We are committed to measuring pupil's progress through primary school and are continuing to look at the best way of assessing children in the early years. We will engage actively with the profession as we do so.
"Parents rightly expect their children to leave primary school having mastered the basics of literacy and numeracy and that is why we have tests at the end of Key Stage 2.
"A high-quality education in English - and the ability to communicate effectively - is an important part of the government's commitment to extend opportunity to all."