The number of Welsh schoolchildren with autism spectrum disorder has risen by more than 50% in the past five years.
Welsh Government figures show there were 3,450 autistic pupils in schools in 2011, rising to 5,325 in 2016.
National Autistic Society (NAS) Cymru said ongoing special educational needs reforms must be used "to make sure the needs of autistic children are always understood".
The Welsh Government is spending an extra £7m on a national autism service.
Figures on the number of schoolchildren with autism spectrum disorder were taken from the annual school census.
The biggest increase was in primary schools, where the figure rose from 1,290 in 2011 to 2,055 in 2016.
'Fulfil their potential'
Secondary school numbers rose from 1,300 to 1,915 and in special schools it went from 855 to 1,300 while figures in nursery and middle schools changed marginally.
Meleri Thomas from NAS Cymru said this was largely due to a better understanding of autism and improvements in diagnostic services, and the growth in autistic children getting support in school was in line with this.
She added: "Four in every five parents who responded to an NAS Cymru survey said their child received additional support at school because of their autism through school action, school action plus or a statement.
"However, only two children in five whose parents responded said they were receiving all the support and provisions outlined in their statement or education plan."
Ms Thomas said special educational needs reforms needed to ensure autistic children "get the support they need to fulfil their potential".
Announcing the extra cash for the national autism service in March, Public Health Secretary Rebecca Evans said it would "help ensure people receive consistent services and get the right support, at the right time, wherever they live".