While declining or flatlining NAPLAN results have become a cause for concern, one tiny school in Sydney's west has bucked the trend to improve its scores dramatically in both literacy and numeracy.

The latest NAPLAN results showed the proportion of students meeting national minimum standards in all domains has flatlined or declined for most year groups, and were described as a "wake-up call" by federal Education Minister Simon Birmingham.

However, Christadelphian Heritage College in Kemps Creek is one of 81 schools in NSW, and 330 across Australia, that have been identified by the Australian Curriculum, Assessment and Reporting Authority (ACARA) as showing significant NAPLAN gains in literacy or numeracy, and one of the few schools to improve in both.

The school's principal Felicity Shields said intervening before students start kindergarten and extensive profession development for teachers were the major factors behind its success in the standardised tests, which all Australian students sit in years 3, 5, 7 and 9.

"We have a transition class in term four before kindergarten starts, where students come in one day a week for that entire term," Mrs Shields said.