The authority that runs NAPLAN will investigate problems with the test after a “substantial” number of students scored zero because they found the test confusing.

The Australian Curriculum, Assessment and Reporting Authority (ACARA) is investigating claims that many teachers wrongly anticipated the style of the writing test, with a notable slip in NAPLAN literacy results, according to a News Limited report.

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Writing performance has continued to decline across the board since 2011, with students in grade 3 and grade 5 suffering the greatest drop in marks.

The same persuasive-style question was used across all year levels, with younger students finding it especially difficult to answer the question.

There was a “substantial increase” in the number of students who scored zero for the writing question, which indicates that they didn’t attempt the question or their answers were too poor to be graded.

One of the main criticisms of NAPLAN is that teachers coach students specifically for the test at the expense of the curriculum.

ACARA chief executive Robert Randall concedes the question may have been confusing for some primary school students.

But he also says the results may indicate schools are teaching to the test and students performed poorly because they were wrongly prepared for a narrative piece.

“Rather than be beholden to the model we were given when we inherited NAPLAN … we will look to improve it and make it line up with the curriculum better,” said Mr Randall.

– with AAP