This chapter illustrates the main results of a language laboratory held in a Montessori primary school in Milan, Italy, during 7 years. Pupils (age: 9-11) are guided in the collective invention of a secret language, using all their linguistic repertoire present in classincluding minority and home languages. The structure of the language is highly influenced by the language of instruction (in our case, Italian), but, at the same time, it differs from that because its aim is to be secret. In other words, the invented language is shared among the class members only, who know how to decipher its alphabet and grammar, unlike other schoolmates. Secrecy permits the inventor to insert elements from other languages, resulting in an a priori language contact. During the process of invention, participants increase their metalinguistic awareness and thus their understanding of the languages they are studying formallyin our case, Italian and English. The Montessori method fosters a "learning-by-doing" approach and an active