In future, students will be required to pass tests in reading, writing and numeracy before they can receive their NCEA qualifications at all levels.
Students can resit them as many times as needed, but principals fear there will be some students who are unable to achieve the standards and will no longer be eligible for NCEA.
The assessments were introduced last year from year 10, with students able to sit the assessments in May and September.
Kaiapoi High School piloted the co-requisites for two years prior to last year's nationwide rollout.
Principal Jason Reid is among those concerned some students will be unable to achieve the literacy and numeracy standards.
"I put out a public service announcement to parents and employers because we may need people to look beyond whether students have NCEA.
"A student may not have NCEA because they missed numeracy [or literacy], but they may have some credits, so have a look and see what they did pass."
Staff have developed literacy and numeracy courses, which will be taken by year 9 and 10 students this year.
Courses will also be available for year 11 to 13 students who have not achieved the standards.
Rangiora High School board of trustees presiding member Simon Green said literacy and numeracy were the foundation subjects, but it would take time to see improvements.
Principal Bruce Kearney said his school's results were similar to the rest of the country.
"We need to keep an eye on whether they pick it up in year 11, otherwise there is a danger students will leave school with no qualifications.
"There is a baseline of literacy and numeracy we need to function and we need to make sure as many get it as possible in year 10 and support those who don't."
Rangiora New Life School principal Stephen Walters said his students exceeded expectations, with 80% pass rates in numeracy and reading, and 96% in writing.
"We had a real focus on the year 10s [last year] with literacy and numeracy and it shows in the results.
"There are opportunities for those in year 11 to pick up literacy and numeracy credits in other subjects, but we aim for most of them to get the co-requisites in year 10."
Nationally, more than 100,000 teenagers attempted at least one of the tests in numeracy, writing and reading over the two rounds.
In September, North Canterbury principals raised concerns after the New Zealand Qualifications Authority took nearly three months to give feedback to schools after the May assessment.
They said it left little time to help students prepare to resit the tests.
Nationwide, about 55% passed numeracy, 66% in writing and 70% in reading by the end of the year.
Until the end of 2027, students can achieve literacy and numeracy standards from other subjects.
New Zealand Qualifications Authority deputy chief executive Jann Marshall said students working towards NCEA level 1 had multiple opportunities to achieve these standards.
Several tertiary education providers were also accredited to offer the standards.
"Students who did not achieve the co-requisite but did achieve enough other credits to attain NCEA will receive the qualification once they have met the co-requisite requirements."
LDR is local body journalism co-funded by RNZ and NZ On Air.
