Almost 7,000 children across Northern Ireland have been sitting the first of this year's unofficial transfer tests.
It is the second year that schools have run their own tests, in the absence of the government-run transfer test.
Two separate organisations are operating tests. The first of three exams for the Association for Quality Education (AQE), takes place on Saturday.
A test for entrance to Catholic grammar schools will take place on 20 November.
The 6,800 children. who will tested at 34 centres in Northern Ireland on Saturday, have already been offered familiarisation visits to the grammar schools where they will sit the tests.
In the past, the 11-plus took place in children's own primary schools.
Over the next few weeks, the system operated mostly by Catholic grammar schools will run tests for 7,000 pupils and the AQE will set two more exams.
Some children will sit both versions, to keep their options open.
The two groups have been negotiating to find a single test and it is understood they may discuss a solution in the new year.
The AQE tests are for children applying to non-denominational grammar schools.
AQE said that the numbers sitting the test this year have decreased slightly compared to 2009.
The association said it expects 6,817 to sit the test on Saturday compared to just over 7,000 children last year.
However, it pointed out that this year the number of children in primary seven in Northern Ireland is 1,000 fewer than in 2009.
BBC Northern Ireland education correspondent Maggie Taggart said that the next four Saturdays would be hectic for some children with some of them sitting three sets of exams.
Ronnie Hassard of the post-primary consortium and principal of Ballymena Academy said there were plans in progress to streamline the system.
"We would much prefer a single test," he said.
"We're working with the current transfer system as best we can. We are working on a single platform and early in the new year we would be hoping to have some proposals for schools."