More pupils are being entered into harder national curriculum tests designed to encourage high achievers, according to official figures.
The government claims the fact that the number of primary school children taking the tests has doubled in two years shows schools are taking advantage of the opportunity to ensure their brightest pupils are stretched.
Sats are taken by 11-year-olds in England, testing their abilities in maths and English. Statutory national curriculum tests assess how youngsters are working at levels 3, 4 and 5. Last week, 550,000 11-year-olds took the Sats exams.
A more difficult 'upper' level six was reintroduced in 2012 after being abolished in 2002. It is now optional, but the figures show many schools are choosing to enter their children for the tests.
In reading, some 95,000 pupils were entered for the optional level six tests, compared with 47,000 in 2012.
While 55,000 children were entered into the level six maths tests in 2012, 106,000 are set to take this year's assessments.
This year, 90,000 pupils were entered for level six tests in grammar, punctuation and spelling, compared with 58,856 in 2013.
A Department for Education spokesman said the tests were reintroduced to ensure those in teaching jobs have the opportunity to "set high aspirations for pupils in literacy and numeracy".
"We want to see every school stretching all their pupils - and these figures show that primary schools have embraced the opportunity to stretch their brightest 11-year-olds by teaching them more demanding new material, in line with the new curriculum, and by entering them for the Level 6 test."
He added that a number of other measures have been put in place to ensure children start secondary school with the best chance of succeeding, including making existing primary school tests harder, raising the bar and introducing higher floor standards.
Sats were introduced for seven-year-olds in 1991 and for 11-year-olds in 1995.