Newly minted Labor backbencher Alannah MacTiernan has hit out at the NAPLAN testing, saying it masks the true illiteracy rate in Australia.

"It does not seem too bad when we say 91.8 per cent of Western Australia's year 3 students achieved or exceeded the national benchmark for reading or 92.3 per cent exceeded the benchmark for spelling," the new MP for Perth wrote in an opinion piece published in The West Australian newspaper this weekend.

Students sitting the NAPLAN test. Credit:Marco Del Grande

"That is until one learns what the national benchmarks are.

"To meet the 2013 national benchmark for reading, a year 3 student has to only answer eight out of 36 questions correctly. To meet the standard for spelling, only three correct words out of 25 words are required. In 2011, one correct answer out of 25 was enough to get a student across the line."