The Scottish Government was accused of “taking its eye of the ball” after literacy among school pupils slipped last year.
Education Secretary Angela Constance admitted that school results were “not as good as they should be” and announced measures to improve reading and writing.
The Scottish Survey of Literacy 2014 found that 55% of S2 pupils were doing well, very well or performing beyond their level they were being assessed for in writing, down from 64% in 2012.
In P7 performance fell from 72% to 68% in 2014, while P4 remained level at 64%.
Reading performance among S2 slipped from 84% to 80% over the two years, while P7 was down from 90% to 88% and P4 down from 83% to 78%.
Pupils from the least deprived areas outperformed those from the most deprive areas.
Scottish Conservative education spokeswoman Liz Smith said the figures showed that when it came to closing the attainment gap the SNP were “failing Scotland’s schools”.
“The SNP’s obsession with trying to break up the United Kingdom has meant that it has completely taken its eye of the ball when it comes to education and helping those from the most deprived backgrounds to succeed,” she said.
“The statistics also tell us that the number of young people doing well and very well in reading has declined. That is something which parents will find totally unacceptable.”
Scottish Liberal Democrat education spokesman Liam McArthur said the performance figures would “set 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,” he said.
“Given the crucial importance of literacy and numeracy skills to our children’s life chances, ministers need to get their priorities right.”
The education secretary said she had asked Education Scotland to strengthen the focus on literacy as part of school inspections, and she planned to “work closely with education partners to establish a national improvement framework.
“Put simply, while Scottish pupils perform well, these results are not as good as they should be,” Ms Constance said.
“They demonstrate the need to redouble efforts to ensure that every child can succeed in school and so gain the skills they need for life.”