The campaign group Cymdeithas yr Iaith says local authorities should now be forced to plan how they help to deliver one million Welsh speakers by 2050.
New data from the group shows that by that date 19 out of the 22 councils in Wales will need to ensure that the majority of the youngest children are in Welsh medium education.
The research claims that by 2040 more than three-quarters of seven-year-olds will need to be in the Welsh medium sector if the government target of a million speakers by the middle of the century is to be met.
This would have far-reaching consequences for all schools across the nation, with secondary schools having to improve the “continuity” in Welsh teaching after transition and facing pressure to improve the provision of Welsh.
Toni Schiavone, Cymdeithas yr Iaith’s education spokesman, said: “In a number of counties, the fact that many pupils don’t continue in the Welsh-medium sector after primary school is the main challenge.
“In counties like Gwynedd, abolishing the option of sitting the second language qualification is a vital part of improving the situation, as it will end the possibility of the system allowing pupils to lose their ability to speak the language. The lack of continuity between Welsh-medium primary education and secondary schools is a major problem in a number of areas, particularly in the west and north.”
The group said the government’s plan to replace second-language Welsh with a single Welsh qualification for every child by 2021 must be implemented.
It also stated that more teachers must be trained to teach through the medium of Welsh, action was needed to stem migration out of Wales, and work was required to normalise use of Welsh in everyday life.
According to the report, in Bridgend the percentage of seven-year-olds taught in Welsh would need to more than treble, with similar increases needed in Cardiff and Swansea.
Mr Schiavone said local authority Welsh medium education plans were “insufficient to say the least”.
He added: “The government must consider a system which sets targets for local authorities which include a minimum of Welsh medium provision. We believe that the system should force local authorities to plan how they will deliver on those targets in order to create the million Welsh speakers nationally.”
He added the targets in the report were the “absolute minimum” which could be set in order to reach the million speakers target.
“Indeed, there’s a strong argument that one needs to move more quickly and further,” he claimed.
A Welsh government spokesman said: “The final language strategy will set a strong long-term direction including a series of indicators to monitor progress towards achieving a million Welsh speakers and increased use of the Welsh language.
“This is not only about education, it’s about increasing and sustaining widespread goodwill towards the language.
“Reaching a million speakers is a deliberately ambitious target. There are challenges ahead but we are building from a position of strength.”