The Qualifications Authority is capping the daily number of students who can sit crucial online NCEA tests next month.
It is trying to avoid a repeat of last year's failures when the online exam system failed to cope when the number of log-ins reached about 18,000.
It has told schools a maximum of 20,000 candidates will be allowed to use the system at any one time, a situation it said could happen on four of the 10 days set aside for the tests.
Students must pass the literacy and numeracy tests before they can receive any NCEA qualification and about 165,000 are due to sit them this year.
Secondary school principals have been told the online exam system has been updated since last year's problems, but the Qualifications Authority is still testing the update and is not sure it will be used in the May testing window.
Secondary Principals' Association president Vaughan Couillault said the success of the tests was "extremely critical" and everyone involved was a little anxious.
"We certainly don't want the situation that we had at the tail end of last year and indeed in that first practice set of the lit/nums where people were unable to access that assessment and it really caused people some distress and duress," he said.
"We really want it to be as seamless as possible so it is mission critical this one."
Couillault said everyone in the sector was a little nervous about the May tests.
"I suppose if the testing on the 2024 iteration is 100 percent positive then we might sleep a little bit easier but that testing just hasn't completed yet."
He said he was happy to work with the Qualifications Authority's requirements if that ensured all schools and students had a good test experience.
Qualifications Authority deputy chief executive, assessment, Jann Marshall said the vendor of the digital assessment platform used for NCEA exams, Oxford-based company RM, had updated it since last year's problems.
"While the vendor of our digital assessment platform has assured us the capacity of the platform has been expanded since November 2023, we are taking a cautious approach," she said.
Marshall said NZQA was conducting its own tests of the updated exam system.
"The number of concurrent users the platform can support will depend on the version deployed in May, and that will be determined by the current testing. Irrespective of the version used, NZQA believes it will be important to manage traffic to some degree," she said.
Information from schools indicated about 20,000 students were intending to complete the online literacy and numeracy tests on four mornings during the May assessment window, Marshall said.
"NZQA is working with a number of schools who plan to offer assessments during these times to see if there are other times within the two-week window which could work for them," she said.
"We anticipate the digital assessment platform being able to comfortably manage more than 20,000 students before the 2024 end-of-year exams begin."