NAPLAN results released on Wednesday show the state only met the national benchmark in three out of 20 categories.

Those categories were grade 3, 5, and 7 numeracy.

All grade 3, 5, 7 and 9 students are tested in reading, persuasive writing, spelling, grammar and punctuation and numeracy as part of NAPLAN.

The test is a measure through which schools, states and territories can determine whether education programs are working and which areas need to be prioritised for improvement.

Tasmania rated second last in 10 of the 20 categories, a slight improvement on ranking second last for 11 categories in 2014, and 14 of the categories in 2013.

Grade 9 numeracy was the only category where the state ranked in front of Victoria.

Individual schools' 2015 NAPLAN results were also released on the My School website on Wednesday.

According to the Australian Curriculum Assessment and Reporting Authority, 25 Tasmanian schools demonstrated substantial improvement in results as student cohorts progressed between years 3 to 5 and years 7 to 9.

Northern schools to demonstrate substantially above-average gain were Longford Primary School, for year 3 to 5 reading, Riverside High School for year 7 to 9 reading, Lilydale District School, for year 3 to 5 reading and Launceston Christian School for year 7 to 9 reading.

Education Minister Jeremy Rockliff said it was encouraging to see some improvements in results, but it was clear a lot of work still needed to be done.

"To improve education we must make targeted investment, structural change and prioritise students with the greatest need, and that's what we're doing," he said.

"There is no greater example of this being targeted than our $17.75 million Learning in Families Together initiative, which is helping 8500 students in kinder to year two, with greatest need at 80 schools this year."