The education system is failing autistic children and changes must be made to help teachers understand developmental differences, an autism advocate says.

Social stigma, intolerance and ignorance held back children suffering from varying degrees of autism, Autism New Zealand chief executive Alison Molloy said on the eve of Autism Appeal Week.

"Children with autism are being disadvantaged because many schools only see behavioural issues, and do not understand developmental differences, or have the strategies to improve the learning outcomes of these students," she said.

"An alarming number of parents are withdrawing their children from mainstream learning environments in favour of alternative schools and learning from home."

One in 100 New Zealand children suffer from some form of autism, which affects social and communication skills and development.

Ms Molloy said many sufferers, especially those with high-functioning autism or aspergers, could achieve in a mainstream classroom with knowledgeable and supportive teachers.

"These children often love detail and order, and need certainty to be comfortable with learning," she said.

"Changes or transitions can be most unsettling and trigger behavioural issues. By understanding these triggers, the children have a better learning experience and teachers avoid having to manage the classroom consequences, which can be significant."