Putting children in an immersion situation so that they learn additional languages has been practiced for 2000 years. Romans had their children instructed by Greek pedagogues so that they learned Greek; the Russians and the English of the 18th century upper-class engaged “Mademoiselles” and “Fräuleins” so that their children would become multilingual. Immersion at school is more recent; it started in Canada in the 60ties, and is currently implemented in many schools around the world. The experience thus gained has made it possible to develop programmes that guarantee the rapid success of immersion.
The central issue in order to reach real bilingualism is continuity: even when a child has become bilingual at 10 years (see Aries Roessler, Bilingue à 10 ans, c'est possible!), they will have attained a B1 level, (intermediate – get’s by in most situations), and not yet a C1 level that would make them fully bilingual (this is reached at 15 years). Complete acquisition of a language continues during adolescence, and this is as true for the second language as for the mother tongue, and stopping language learning at 10 years means that this level will not be exceeded or that the student will regress and forget.
Just as there is a time span during which we spontaneously learn to walk, there is a “linguistic window” during which we spontaneously learn languages. This window opens at birth and progressively closes between 8 and 10 years. When a child is twelve, language development is normally over and the brain moves on to perform other tasks. During the “linguistic window” span, the child just absorbs grammar structures and pronunciation effortlessly. Once bilingualism is acquired, learning other languages is much easier.
Most human beings on earth speak more than one language – Europe’s current monolingualism is an historic exception due to the national movements of the 19th century. Using a language can however reach from the simple ability to pronounce a few standard phrases to the capability to write texts or hold conferences in the second language (Complete active bilingualism). Everybody has experienced this during a holiday: it is quite easy to develop basic passive bilingualism, to understand a few sentences, to pronounce a few words. What takes time is to become actively bilingual.