Twelve out of the 23 11-year-olds at Whitings Hill primary, in Hertfordshire, missed their national tests with what their head believes are stress-induced illnesses.
Richard Maudsley said the pupils due to take the tests were ill during exam week.
Mr Maudsley said: "Putting chilren this young, under this much strain is just not right. They are not only expected to perform well for their own self-worth, but also for parents, teachers and the school in general.
"At the end of the day if they don't do well this shows in where we stand in the school league tables. We are risking creating a generation of nervous children to boost government statistics."