There was a rise in the number of allegations of malpractice in tests for seven, 11 and 14-year-olds, but fewer schools had results quashed than last year, the Qualifications and Curriculum Authority has announced.
It investigated 479 cases of malpractice this year and quashed results in seven English schools, less than 0.02 per cent of schools.
In 2001, 270 cases were investigated and 11 schools had results in at least one subject quashed.
A QCA spokeswoman said: "We have full confidence in the professionalism of teachers.
"QCA works very closely with local education authority inspectors who conduct thorough checks throughout the test process.
"A decision to annul the results of the school is only taken where we cannot guarantee that work is the unaided and independent work of the pupils."
Her comments followed fresh allegations of widespread cheating in the tests taken by 11-year-olds, which are used by parents and local education authorities to judge primary schools' performance.
Practices such as allowing extra time, sitting pupils together, reading questions out in a particular way and suggesting that pupils check wrong answers are widespread, it is claimed.
Phil Willis, the Liberal Democrat education spokesman, said: "Our education system relies far too heavily on external testing, giving rise to suspicion and anxiety about performance and league table position.
"A system of 'chartered examiners' should be instigated. Schools could promote a teacher to be trained professionally for administering exams.
"They would be the examination authority in their school, providing quality control, and would be paid appropriately."