New Zealand's 13-year-olds have recorded their worst-ever results in a major international maths and science test.
The Year 9 students' scores in the Trends in International Mathematics and Science Study (TIMSS) fell by the largest margins since the study began in 1994.
More than 580,000 children in 64 countries participated in the test in 2019.
Singapore topped the table in every subject and for every age group with average maths scores of 625 for nine-year-olds and 616 for 13-year-olds, and science results of 595 for nine-year-olds and 608 for 13-year-olds.
New Zealand's scores for nine-year-olds (Year 5 students) also fell in both subjects since the last time the test was conducted in 2014/15.
But Year 9 students' results were particularly bad. Their maths score fell 11 points to 482 and their science score fell 14 points to 499 on a scale where 500 is the midpoint.
The study showed the students performed worst in algebra and chemistry questions, and best at data and probability, and earth science.
It found New Zealand had one of the biggest achievement gaps in maths based on the number of books students had at home with 90 percent of students with lots of books meeting or exceeding the study's benchmark for low performance, while the figure for students with few books at home was around 60 percent.
The directors of the study, Dr Ina V S Mullis and Dr Mick O Martin, from the Lynch School of Education at Boston College in the United States, said the decline in New Zealand's 13-year-olds' results were "a little startling".
They said the results showed a "probably insurmountable gap" in maths achievement between Asian countries and the rest of the world, and that children's home environment had the biggest impact on their achievement across all countries.
Martin said New Zealand had one of the highest, if not the highest, use of technology in schools.
Education Ministry chief scientific advisor Professor Stuart McNaughton from the University of Auckland said the scale of the drop in 13-year-olds' scores had surprised him.
"It's quite significant to be honest," he said.
McNaughton said the TIMSS report showed where New Zealand students were weakest, such as biology and statistics, and that would help with targeted solutions.
"These are really tough challenges and to be honest we should have solved them but we're now in a better position to do that."
He said the Year 9 scores were the cumulative result of teaching in Years 4-8.
He said it was worth making the effort to try and improve New Zealand's scores, particularly because schools should ensure that Māori and Pacific children achieved as well as other children.
McNaughton said it remained to be seen if the latest results were a trend that would be continued.
"It does tell us that what we have been doing hasn't been working," he said.
"We now need, I think as an example, more specialist teaching in Years 4-8."
New Zealand's Year 9 students' maths results showed the re-emergence of a gap between boys' and girls' performance (in favour of boys) and 18 percent of the students failed to reach even the low-performance benchmark while only six percent reached the advanced benchmark.
By comparison, in Australia only 10 percent of students did not reach the low benchmark, and in Singapore 51 percent achieved the advanced benchmark.
In science, just eight percent of Year 9 students reached the advanced benchmark, well behind the best-performing nation, Singapore, where 48 percent of students were advanced.
New Zealand's Year 5 students scored 487 points in maths performance and 503 points in science. Both results were lower than the previous tests but little different from results for their age group during the past 20 years of testing.
At both year levels and subjects, students at schools in rich communities did better than students in poorer communities, as did students who reported a high sense of belonging and students that went to schools that emphasised academic success.
Seven percent of the New Zealand students said they were bullied weekly, 28 percent said monthly and 64.5 percent said never or almost never. Those figures were similar to Australia, and slightly worse than in England and the USA. The study found students who were bullied daily or weekly had lower scores than students who reported little to no bullying.
Compared to other countries, New Zealand's scores ranked as follows (with the previous 2015 ranking in brackets) Year 4 maths 40th (34th), Year 4 science 34th (32nd), Year 9 maths 23rd (21st), Year 9 science 19th (16th).
The study is run by the International Association for the Evaluation of Educational Achievement.
Last year, New Zealand's 15-year-olds recorded their lowest scores ever in the OECD's Programme for International Student Assessment (PISA), which tests reading, maths and science. Of the 79 participating countries in PISA, New Zealand was 11th equal for reading, 12th for science, and 27th for maths.
Setting the benchmarks
To reach the TIMSS benchmarks, students had to correctly questions like the following:
Maths: Year 4 students, advanced benchmark
A teacher wants to put 30 students in groups so that each group has the same number of students AND each group has an odd number of students. Show two different ways the teacher could make the groups.
Answer: Six groups of five students; 10 groups of three students.
(21 percent of New Zealand students answered this question correctly. The international average was 24 percent.)
Science: Year 4 students, low benchmark
Which animal has a backbone: octopus, spider, butterfly, frog.
(78 percent of New Zealand students answered this question correctly. The international average was 74 percent.)
Maths: Year 9 students, intermediate benchmark
On Thursday, the lowest temperature in City X was 6 degrees C and the lowest temperature in City Y was -3 degrees C. What was the difference between the lowest temperatures in the cities?
Answer: 9 degrees C.
(69 percent of New Zealand students answered this question correctly. The international average was 59 percent.)
Science: Year 9 students, intermediate benchmark
Show whether each symbol or formula represents an element or compound.
Answer: Element, element, compound, compound, compound, element.
(48 percent of New Zealand students answered correctly. The international average was 61 percent.)