After the creation of Israel in 1948, ulpans (or ulpanim) were set up for the intensive study of Hebrew. Today, ulpans still exist; they are institutes or schools "designed to teach adult immigrants to Israel the basic language skills of conversation, writing and comprehension" (quoted from Wikipedia).
Again according to Wikipedia,
The ulpan framework has been adopted by other nations attempting to revive their own declining or lost languages. Wales, Scotland, and Norway have used the ulpan model for native language instruction.
For example, Ulpan.co.uk, a site where you can learn Scottish Gaelic, writes:
The same method of teaching has been used successfully in Israel, Wales and beyond where it has brought thousands of learners to fluency in their respective languages.
And for the use of ulpans in Wales, see e.g. the article The Ulpan in Wales: A Study in Motivation (Journal of Multilingual and Multicultural Development, 1991).
For the ulpan model in Norway, see Norwegians hope to translate Hebrew revival into their own miracle (March 2012). For the Sámi language, see Laplanders turn to Israel to learn Sámi (February 2012).
(The revival of Hebrew started at the end of the 19th century, roughly half a century before the establishment of ulpans.)
If the ulpans were seen as so successful that they were used as a model for reviving other languages, has there been any research on what made them effective? Did they have a specific teaching approach or specific teaching methods that had not been used elsewhere? Did they combine existing language teaching ideas in a new way?