Matthew MacIver, registrar of the General Teaching Council for Scotland, told a primary teachers' Gaelic conference in Stirling last week that immersion teaching was "at a plateau".
Mr MacIver said: "The shortage of teachers is not going to be met by conventional methods. We have to look at other means of providing a teaching force for Gaelic. Up till now we have been looking at Gaelic native speakers but they are not there any more."
His views were echoed by Rosemary Ward, a member of Bord na Gaidhlig, the new development agency for Gaelic, and an education official in Argyll and Bute. "Gaelic-medium education will never give us the critical mass we require. It will not address that alone," she said.
Professor Dick Johnstone of Stirling University, a renowned researcher on languages, said the country could "not rely on GME".
Ministers have repeatedly accepted that Gaelic-medium education remains their favoured route to halt the rapid demise of the language and it features strongly in the draft Gaelic Language Bill which will later this year grant official recognition to the language.
Under the new legislation, education departments would be compelled to draw up plans to support Gaelic and will be held to account for them. Ministers have promised to get tough if they are not satisfied with progress.
But some lobbyists are pressing for alternatives and want Gaelic to be taught by class teachers trained in a similar way as those who have gone through the Modern Languages in Primary Schools (MLPS) programme. Teachers volunteer to study a block of the language over 20-plus hours and are then qualified to teach Gaelic for up to an hour a week.
Some eight local authorities are working on the first phases of such a programme and early results are positive. Gaelic is assuming equal billing alongside French and German in the pilot primaries and is supported by a substantial body of international evidence which shows that students gain by learning several languages.
But Duncan Ferguson, chair of Bord na Gaidhlig and headteacher of Plockton High, insisted there had always been a twin-track approach and that Gaelic-medium education for as many as possible remained the long-term aim.
"I hope this is not a change of tack but an acknowledgement of a shortage of teachers. As a board, I still think our main focus is Gaelic-medium education in primary and secondary," Mr Ferguson said.
Bruce Robertson, Highland's education director, who has been at the forefront of a Gaelic revival in schools, welcomed the change of emphasis.
"I can see this as being a natural development of the Gaelic language in primary and secondary schools," Mr Robertson said. "Only so many parents will take the leap of faith to provide Gaelic-medium education for their youngsters.
"But there are many parents who would be willing to support Gaelic as a second language in primaries and secondaries. It's very popular in Highland and I'm delighted to hear there is support for it."
Mr Robertson believes there may be alternative ways to train teachers, other than the MLPS model. Universities and Sabhal Mor Ostaig, the Gaelic college in Skye, might devise distance learning courses that could be approved as part of teachers' continuing professional development.
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