TORONTO — Critics say the backlog of autistic children waiting for crucial therapy in Ontario is growing at an alarming rate and in some cases leaving parents to pick up the tab for costly treatment.

NDP Leader Andrea Horwath says as of March 31, there were 1,513 children waiting for treatment -- up 450 from December.

She says 389 children were waiting for assessments in that period, while at the end of last year 102 children had their services terminated.

Horwath says that as waiting lists grow, parents are paying out of their own pockets to obtain services such as Intensive Behavioral Intervention, or IBI.

She says a pilot program to bring IBI into schools still does not exist and is calling for regular, public reporting of wait-list numbers.

The government came under fire earlier this year when it was accused by critics of arbitrary cutting off funding to children in need of IBI to reduce wait lists.

It has denied such a move and said it was had been providing therapy for autistic children and working to improve services.