Teenagers had about 300,000 fewer NCEA results in the bag last month than at the same time last year, according to Qualifications Authority figures.
The figures also show big variations in the way the pandemic has affected NCEA results in different parts of the country.
By 28 October, schools in the Tasman region and in Manawatū-Whanganui had reported a lot fewer results compared to the same time in 2019 than schools in Otago, Nelson and Gisborne.
Nationally schools had reported 22 percent fewer not-achieved results, 18 percent fewer achieved and merit results, and 15 percent fewer excellence results.
The number of achieved, merit and excellence results totalled 1,718,698 - a drop of 359,588 or 17 percent from the same time last year.
In Auckland, which has had two lockdowns that closed schools, not-achieved results were down by 26 percent while achieved results were down 22 percent, merit 20 percent and excellence 17 percent.
The pandemic appeared to have had the least impact on schools in Otago, where achieved results were nine percent lower, merit 11 percent and excellence 10 percent lower.
In Tasman, schools had reported a lot fewer results than at the same time last year with not-achieved results down 37 percent, achieved down 22 percent, merit down 34 percent and excellence down 40 percent.
In Manawatū-Whanganui, schools had reported 22 percent fewer achieved results, 20 percent fewer merits and 19 percent fewer excellence results.
The Qualifications Authority said schools had deferred assessments until later in the year.
"With the 2020 school terms and holidays being altered in response to Covid-19, key reporting dates are later this year than last year. Results will continue to be reported by schools into December," it said.
Secondary Principals' Association president Deidre Shea said the lag in reporting of results was in line with what schools were expecting.
She said the extra learning recognition credits available for students this year would give many students enough credits to ensure they gained their NCEA qualifications.
The credits give students in Auckland up to 20 percent of the credits required for an NCEA certificate, and up to 13 percent for students elsewhere.
The principal of the largest secondary school in the Tasman district, Scott Haines from Waimea College, said he was not aware of any particular problems with student achievement in the area as a result of the pandemic.
He said the relatively low number of results reported by the region's schools was most likely due to delays in assessment and reporting of results, and his own school recently sent a large number of results to the authority.
Haines said some students had not engaged well with learning since the alert level 4 lockdown earlier this year, but others had risen to the challenge.
Nationally, the figures showed little difference between Māori, Pākehā and Asian results though Asian students had only 13 percent fewer excellence results than last year.
Pasifika students reported a bigger drop in not-achieveds and achieveds than other groups at 25 percent and 20 percent respectively, but a smaller drop in merit and excellences than other groups at 15 and 12 percent fewer results than the same time last year.
There was no clear pattern when schools were considered by decile, though the number of excellence results reported by decile one and two schools were only nine and 11 percent lower than last year respectively.
The figures showed that the percentage of not-achieved, achieved, excellence and merit results was near identical to last year.