Questions are being asked after the exodus of several board members from the National Disability Insurance Scheme.

National Disability Insurance Agency (NDIA) CEO Robert De Luca resigned on April 30 to take a new job as the head of community health organisation Zenitas Healthcare.

The NDIA deputy CEO for strategy development and the head of markets, provider and sector development have also left in recent weeks.

The executive in charge of participants and planning experience is due to leave in September.

“If minister Stuart Robert says NDIS going so well ... then why am I hearing that four senior staff have resigned in the last seven days?” Labor's disability spokesman Bill Shorten tweeted this week.

Mr Robert talked up the success of the scheme on Thursday.

“Since the government was elected, the prime minister and I have been speaking first-hand with participants, families, carers, advocates and providers to hear first-hand how this world leading scheme is improving outcomes for participants,” he said.

“We are 80 per cent of the way and we recognise the last 20 per cent can sometimes be the hardest.”

A spokesperson for the NDIA said the agency continues to have a “strong and experienced leadership team, who are focused on continuing to guide the agency to deliver improved outcomes for NDIS participants”.

“To ensure the important work of the NDIS continues, interim arrangements with experienced personnel have been put in place.”