Ronnie Smith, general secretary of the Educational Institute of Scotland, said: "It does little to support quality teaching and learning and could impede the successful delivery of A Curriculum for Excellence in schools."
The EIS stance on testing puts it at loggerheads with the Association of Directors of Education in Scotland whose outgoing president, Bruce Robertson, recently called on the Scottish Government to bring back the publication of national attainment data as part of a new performance framework.
Mr Smith claimed that the end of formal national tests in 2002-03 and the subsequent introduction of the Scottish Survey of Achievement (SSA), which samples only some pupils' work, had "failed to quell many education authorities' desire to submit pupils and teachers to an excessive testing regime".
Some authorities continued to favour the "flawed 'league table' approach to measuring school success", he said.
"This is in direct contradiction to current national educational priorities and has a negative impact on learning and teaching in schools.
"The use of such widespread testing places additional pressure on pupils and teachers to perform well in these tests. This has the inevitable result of narrowing the scope for teachers to use their professional judgment in what they teach, with considerable pressure to 'teach to the test' to avoid criticism of the school when league tables are constructed."
Such a "tick-box approach" to measuring school success was of little value and served only to provide figures for education authority statisticians to crunch while simultaneously demoralising pupils and teachers, Mr Smith added.
The introduction of the SSA and the development of national assessment banks containing associated materials had been intended to simplify and improve the process of testing, he claimed, but had largely failed to do so.
The materials held in the national assessment banks were of questionable value, added nothing to the educational process, and continued to undermine the judgment of teachers by removing their role in determining appropriate methods of assessing their own pupils' progress in the classroom.
Mr Robertson countered, saying: "The signing of the concordat between COSLA and the Scottish Government gives all of us an opportunity to review how we measure performance in education and children's services.
"I would agree that excessive testing should be avoided, but we must be able to answer a justifiable question: how good is Scottish education across the country and beyond? A mature debate is required which must take into account the needs of all the stakeholders, of which teachers are one part."
A spokeswoman for the Scottish Government said: "In light of the concordat, we will be reviewing the Scottish Survey of Achievement in discussion with local authorities as part of a broader review of requirements for (and use of) performance management information.
"It is important that the tools we use for performance management reflect and support the learning we value in Scotland."
She said the Government was committed to reducing bureaucracy and any assessment that got in the way of learning and teaching.
"Appropriate and proportionate assessment, however, underpins good learning and teaching, and is an essential tool for teachers in helping children to progress and in reporting achievement to parents," she said.
Assessment tools and methodologies would be reviewed as part of the overall Curriculum for Excellence programme to ensure that assessment meets the needs of the new curriculum, said the spokeswoman.