The education system needs to be "radically changed" to reach the Welsh Government's target of having one million Welsh speakers by 2050, the language commissioner has said.
Meri Huws said all children under seven need to be immersed in Welsh.
She said Wales should earmark a window of five or 10 years to generate enough teachers - and local authorities need to be given the resources.
The Welsh Government said work was already being done.
Ms Huws told BBC Radio Cymru: "I would expect us to reach a million speakers. That's the aim, that's what the Welsh Government has said is going to happen and I'm hoping it does.
"I don't see why it shouldn't happen as long as we start planning it today.
"If we are completely serious about reaching a million, we need to radically change the education system from now on."
She said Wales had lost its way to some extent with teacher training which needed to change.
Welsh Language Minister Alun Davies said: "We are currently developing the new #Cymraeg2050 Language Strategy which will include a series of indicators that will enable us to monitor progress towards achieving that goal.
"It will build on the current Welsh Medium Education Strategy and include targets for expanding and improving education provision."
There were plans to increase the number of Welsh teachers, he added.