Fewer 14-year-olds have reached the standard expected of their age group in English tests this year.
Science and maths results improved this year
The proportion of pupils in England reaching the national target level fell by two percentage points to 72%.
A third failed to make this grade in reading tests, the Department for Education and Skills said.
However, results for maths improved, with 77% of pupils meeting expectations (up three percentage points on 2005), and in science, 72% (up two points).
About 600,000 teenagers took the tests this summer.
The government has set a target of 85% of pupils reaching the expected level.
Schools Minister Jim Knight said: "I want to congratulate pupils, parents and teachers for their hard work over the last 12 months."
He added: "However, I'm concerned that English has fallen this year following the very good progress seen last year and despite a 15 percentage-point increase since 1997.
"We cannot afford to be complacent and need to redouble our efforts to reverse this next year."
In reading, 59% of 14-year-old boys reached the expected standard, compared with 74% of girls.
In writing, 83% of girls did so, compared with 69% of boys.
Meanwhile, in maths, 77% of girls achieved the expected levels, one percentage point ahead of boys.
Overall, maths results rose by three percentage points from 2005.
In science, 72% of pupils reached the expected level for their age - up from 70% last year.
Last month, it was revealed that the government had missed its target of getting 85% of 11-year-olds in England reaching the required grade in maths and English.
Ministers say testing pupils at ages seven, 11 and 14 raises standards, but opponents argue that the regime creates too much stress.
Shadow Education Minister Nick Gibb said: "It is unacceptable that 33% of children at the age of 14 are still not reaching level 5 (the expected standard) in reading.
"This is an absolute minimum standard that all children need if they are to benefit from secondary education and if they are to survive in the increasingly competitive job market in later life."