Secondary headteachers’ leaders will warn current proposals do not amount to a “credible measure” of skills and will lead to an “administrative quagmire” for senior staff.

Carole Ford, president of School Leaders Scotland (SLS), also believes the new measures will fail to increase the number of pupils leaving school with basic skills.

Earlier this year, Fiona Hyslop, the Education Secretary, unveiled plans for new literacy and numeracy assessments from 2012 onwards to respond to long-standing concerns of employers and universities about skills.

Current estimates suggest 25% of the primary school population goes on to secondary without achieving basic literacy requirements – some 15,000 pupils.

Under the plans, classroom teachers will identify three pieces of work that showcase a particular pupil’s abilities, as long as they do not come from English or maths classes.

The Government argues the portfolio, which will be externally marked by the Scottish Qualifications Authority, is a better measure of skills than a single test.

However, critics question whether it will reflect the normal standard of individual pupil performance because teachers are likely to submit pieces of work that demonstrate the absolute best that can be achieved.

There are also concerns that there is no measure of what level of support a pupil has been given from teaching staff.

SLS favours a broader approach that would rely on some course material – but which would also feature a stand-alone test.

Ms Ford is expected to tell the conference: “The proposals for literacy and numeracy assessment will not deliver a credible measure of either skill and will detract from teaching and learning time.

“Most seriously of all, we now face the prospect of no formal measure of either literacy or numeracy until the tenth year of a child’s education, at the earliest.

“We know that the early years of education are the most important in relation to both these skills, yet there is to be no formal mechanism for measuring progress, no standardised means of communicating progress to secondary schools, and no accountability during the first seven years of education.”

Garry Clark, head of policy with the Scottish Chambers of Commerce, echoed the concerns. “What employers want is a measurable standard that is uniform across the country,” he said.

A spokesman for the Scottish Government said detailed arrangements on the new awards had not yet been established.

“We are confident that Ms Ford’s concerns will be addressed through this ongoing development and SLS is engaged actively in the governing group that will oversee this process,” he said.