Nationally one million school students in years 3, 5, 7 and 9 sat the tests in May which examine numeracy, reading, writing, spelling, grammar and punctuation.
About 17,800 students across the ACT took part.
Results show ACT students continue to excel in reading and the ACT has been the highest performing state or territory in Australia every year since 2008.
The ACT also ranked first or equal first for grammar and punctuation and numeracy in NAPLAN testing across all year levels since 2009.
However there has been a drop in the percentage of ACT year 9 students who perform above national minimum standards for numeracy.
The reading and numeracy results for ACT Aboriginal and Torres Strait Islander students were generally higher than those of other metropolitan areas.