The extra security measure ordered by the Government's exam watchdog comes after a number of cheating allegations this summer.
Last month, David Hopkins, head of Whiteknights primary, in Wokingham, Berkshire, resigned when results in maths and science were quashed amid claims of irregularities. A local authority inspector uncovered "problems" on a monitoring visit to the school and alerted the Qualifications and Curriculum Authority.
The TES revealed in May that the constant pressure of league tables has led some teachers to cross the fine line between helping children unused to an exam situation and outright cheating.
This week maths test scores at Greenacre first and middle school in Great Yarmouth, Norfolk, were voided when it emerged that pupils were allowed a 15-minute break in the middle of the test.
Concerns that allegations of rule-breaking could undermine results has also led the QCA to give inspectors secret training in cheat-detection techniques. Now test papers for 1.6 million seven, 11 and 14-year-olds have been redesigned for 2003. A broken seal would show the paper had been tampered with.
Reports of cases of cheating in national tests rose from 147 in 2000 to 270 last year. However, only 11 cases were upheld.
Meanwhile, a teacher appeared before magistrates last Friday charged with stealing five Edexcel GCSE maths papers. Farzana Akbar, 46, who taught community languages at Archbishop Lanfranc school in Croydon, Surrey, was arrested last month after it was claimed pupils in a private tutor group had been shown the paper on the eve of the exam. She was remanded on bail until August 2.