The Conservatives have set out plans which they say will ensure children can read by the age of six.
The Tories say not enough children leaving primary school can read
Shadow schools secretary Michael Gove said English assessments for six and seven year olds should be replaced with a standard reading test.
But primary school head teachers have warned against formal tests for young children saying exams could put them off reading "for a very long time".
Schools Secretary Ed Balls said the plans were "hastily cobbled together".
Chris Davis of the National Primary Headteachers' Association (NPHA) said the tests would come "too early".
"One of the worst things you can do with a very young child is give them the impression that they can't do something," he added.
Other measures are also due to be outlined by the Conservatives in an attempt to narrow the attainment gap between advantaged and disadvantaged children in England.
A key factor in the Tory plans involves extending the use of "synthetic phonics", which focuses on teaching the sounds which make up words.
Mr Gove told BBC's Andrew Marr Show: "We think by the time a child has been through two years of primary school, reception year and year one, they should be able to decode effortlessly, they should have mastered the building blocks of reading.
"Unless they learn to read properly they won't be able to read to learn subsequently, and this is the key foundation stone on which the rest of learning is built.
"We want to introduce a simple test which means at the end of two years of primary school we know whether or not children have mastered the skills they need to read.
"Once children have got that skill, then teachers are free to inspire them, and children are free to read and explore on their own."
Mr Gove added that, currently, 20% of children leaving primary school were incapable of reading, rising to 40% of children from poorer backgrounds.
He said: "These are the children who will go on to truant, who will go on to be disruptive potentially, who will miss out themselves, and will also undermine learning for others."
Mr Balls said the opposition was either calling for measures the government were already pursuing or was looking to turn back the clock.
The government was already clear that phonics should be the "prime approach" in teaching young children to read, he added.
"Today 100,000 more 11 year olds are reaching the required standard in literacy than 10 years ago, but I know there is more to do. That is why we are rolling out nationally our successful Every Child a Reader programme.
"By introducing a new externally-administered test, the Tories would in fact turn the clock back and increase burdens and bureaucracy for every primary school."
Tory leader David Cameron will spell out the party's education policy with the publication of a paper on Tuesday.
Steve Sinnott, general secretary of the National Union of Teachers, said synthetic phonics was useful but the Tories were "obsessed" with it. He said: "They somehow think it is a magic solution for everything else."
John Dunford, general secretary of the Association of School and College Leaders, criticised the move to end appeals against exclusions.
He said: "The reason we don't [support the Tory proposal] is because we have consistently said appeals panels provide the natural justice avenue of appeal."
"If it were not there, it would mean parents would take schools to court and headteachers do not want to spend more time in court defending appeals actions."
Schools Minister Jim Knight said: "This is an own goal by the Tories, their badly thought-out education policies are back-firing once again."