Pupils starting school in the Western Isles this year will automatically be taught in Gaelic.
The new Gaelic First policy has been introduced by the islands council to help boost the use of the language and give children the benefits of being bilingual.
The change means that the default language of education for the local authority will be Gaelic from P1 until P4, unless parents opt out.
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Last year, 47 per cent of P1 children in the area were enrolled in Gaelic Medium Education (GME), with four in 10 primary pupils taught in the language.
The most recent census results in 2011 indicated that 61 per cent of people in the Outer Hebrides had some understanding of Gaelic and 52 per cent were able to speak it.
Western Isles Council education director Bernard Chisholm outlined the new policy in a letter to teachers and parent councils.
Lessons taught in Gaelic
He wrote: "It was agreed at the last comhairle (council) meeting that all children enrolling in Primary 1 for the 2020-21 academic session will be enrolled in Gaelic-medium education unless their parents request that they are enrolled in English-medium education.
"Currently, in many of our primary schools, more than 50 per cent of children are enrolled in GME at P1.
"We want to see this number grow in order that we both retain our language and provide all of our children with the many benefits bilingual children gain through the acquisition of another language."
He asked that the policy is brought to the attention of parents enrolling prospective P1s; some would need to have the benefits explained in detail and be given information on the resources and support available, particularly non-Gaelic speaking families.
In a statement, Mr Chisholm said: "The Outer Hebrides is a Gaelic-speaking community, with a rich Gaelic heritage and culture.
"The majority of our children in nursery and those enrolling in primary want to speak our language.
"A significant number of families who move to the area without Gaelic enrol their children in GME for the additional benefits of bilingual education."
He added: "I believe that we all want our children to access the undoubted benefits that GME provides, in both English and Gaelic, in terms of reading, thinking skills, problem-solving, maths and in many other areas.
"It is truly a free gift and in this increasingly mobile world, it also enables them to acquire other languages much easier."