A survey of hundreds of primary school teachers shows there is not enough support for children with special needs, the Educational Institute says.
The union said 352 out of 800 special education needs co-ordinators responded to its survey, with 89 percent saying their school did not get enough government support for special needs.
Almost half said that meant up to 60 percent of children were not getting adequate help.
The Education Ministry said special education funding had increased by 29 percent in the past six years to $530 million a year, with last year's budget adding about $16 million more per year.
It said about 80,000, or 10 percent, of children received special education help each year.
However, the Educational Institute said its survey showed schools deemed 16 percent of children to have special needs.