Reading standards among eight and nine-year-olds in Scotland have fallen by 5% since 2012, a study has found.
The Scottish Survey of Literacy and Numeracy (SSLN) looked at performance in school years P4, P7 and S2.
It found 78% of P4 pupils performed well or very well in reading in 2014, compared with 83% in 2012.
The Scottish government said work to improve literacy in schools would be stepped up following the results.
P7 pupils also saw a drop in reading performance, with 88% performing well or very well in 2014, compared with 90% in 2012.
And 80% of S2 pupils performed well or very well, a fall of 4%.
For the purposes of the survey, literacy was split in three categories – reading, writing, and listening and talking.
Within each category pupils were assessed into one of four levels of attainment.
These were “Not yet working within the level”, “Working within the level”, “Performing well at the level”, and “Performing very well at the level”.
For writing and for listening and talking there was an additional category – performing beyond the level.
In writing, it found two-thirds of P4 and P7 pupils were performing well, very well or above the level expected, as were 55% of S2 pupils.
In listening and talking, two-thirds of P7 pupils and more than half of P4 and S2 pupils were working well, very well or beyond the level.
Girls outperformed boys at P4 and S2 in reading, and at all three stages in writing.
Pupils from the least deprived areas performed better in all areas of literacy, compared to those from the most deprived areas.
Larry Flanagan, general secretary of the EIS teachers’ union said that while the majority of pupils continued to perform well, there was no room for complacency and teachers were facing added budgetary pressures.
He said: “Whilst it is important to analyse these findings and learn any lessons, the EIS is very clear that particular challenges remain for schools, teachers and pupils.
“For example, we have seen a drop in teacher numbers, a rise in class numbers, teacher workload at an unsustainable level and restrictive budget cuts reducing resources. Both local and national government need to realise that austerity has an impact on our schools and young people.”
Education Secretary Angela Constance said work was already under way to improve standards since the survey was carried out in May 2014.
And she said school inspections would now put more emphasis on raising standards in literacy.
She said: “While Scottish pupils perform well, these results are not as good as they should be. They demonstrate the need to re-double efforts to ensure that every child can succeed in school and so gain the skills they need for life.”
Scottish Labour education spokesman said the Scottish government needed to do more to help pupils from deprived areas.
He said: “In the 21st century every child should expect the school system to provide them with the basic skills in literacy and numeracy they need for their future. They are being let down by this SNP government’s complacent approach to education.
“That’s why Scottish Labour has a plan tackle the attainment gap, committing to spending £125 million over the course of the next parliament, on top of the SNP attainment fund, targeting the communities and schools facing the greatest barriers to attainment and including literacy specialists working with school children, preschool children and their parents.”
Scottish Liberal Democrat education spokesman Liam McArthur said the Scottish government also said standards must improve.
He said: “These results show that the performance of Scotland’s pupils in reading and writing has either stagnated or is going backwards. This will have alarm bells ringing with parents across the country.
“While the SNP focus has been on their independence plans, ministers have taken their eye off the ball in government. Given the crucial importance of literacy and numeracy skills to our children’s life chances, ministers need to get their priorities right. They can start by explaining how they plan to turn around this worrying trend in the literacy standard.”
Scottish Conservative young person spokeswoman Liz Smith said parents would find the results “unacceptable”.
She said: “The Scottish Conservatives believe that all pupils, whatever their background, should be entitled to a good education. Much more needs to be done to focus on reading, writing and numeracy skills across the board and on the proper testing of these essential skills.”