All teaching students in NSW will have to pass a ''tough'' literacy and numeracy test before they can graduate, amid concerns some new teachers struggle to explain maths and grammar concepts to their students.

Students who fail the new online test, which will be introduced by 2016, will not be allowed to complete their final practical assessment in the classroom, which would stop them graduating.

Education Minister Adrian Piccoli said he expected high standards of teaching graduates and the new test would ensure every student graduating from a teaching course in NSW had adequate literacy and numeracy skills.

''The test will be quite difficult, quite complex, and so it should be,'' Mr Piccoli said.

''I don't resile for one minute from setting very high standards and guarding them with things like a literacy and numeracy test.''

Mr Piccoli said universities and schools had reported graduate teachers struggling to explain maths and grammar concepts.

NSW would be the first state to set such a test, with a complete introduction planned for 2016 after trials this year and next. Students would be able to sit the test as many times as they wish - ''a little bit like your driver's test'', Mr Piccoli said.

But Tom Alegounarias, president of the NSW Board of Studies, Teaching and Educational Training, said some students would not be able to pass at all.

''If history and commonsense about tests apply, there will be students who find that they are not suited to teaching,'' he said. Mr Alegounarias said universities should encourage students to sit the tests early in their degrees. but a high failure rate would not necessarily prompt revised, easier questions.

''If students are failing because they don't have the requisite knowledge, that would not be a reason to change the test,'' he said.

Emma Semrani, a fourth year teaching student at the Australian Catholic University, is doing her practical placement at Holy Family Catholic Primary School in Menai.

''We need to ensure that we are competent in what we do so we give children the best chance of the best future possible,'' Ms Semrani, 21, said. ''I think it's important that you as a teacher constantly revisit material to make sure you are up to date.

''You're not always going to be 100 per cent competent in your own literacy or numeracy because you have to teach all key learning areas.''

Mr Piccoli said all of the state's vice-chancellors had agreed to the new assessment, devised by the Australian Council for Education Research and the NSW Board of Studies.

As part of improving teacher quality, students starting a teaching degree from school will also need three Band 5 Higher School Certificate results, one of which must be English.