Language proficiency is the ability of an individual to use language with a level of accuracy that transfers meaning in production and comprehension. There is no singular definition of language proficiency: while certain groups limit its scope to speaking ability, others extend it to cover both productive and receptive language skills and their effective application in varying practical contexts. However, this diversity has implications for its application in other language domains such as literacy, testing, endangered languages, language impairment, etc. There is little consistency as to how different organizations classify it. Native-level fluency is estimated to require a lexicon between 20,000 and 40,000 words, but basic conversational fluency might require as few as 3,000 words. Developing language proficiency Developing proficiency in any language begins with word learning. By the time they are 12 months old, children learn their first words and by the time they are 36 months old, they may know well over 900 words with their utterances intelligible to the people who interact with them the most. Developing language proficiency improves an individual’s capacity to communicate. Over time through interaction and through exposure to new forms of language in use, an individual learns new words, sentence structures, and meanings, thereby increasing their command of using accurate forms of the target language. Issues in defining language proficiency Languages that are considered endangered are undergoing efforts to revitalize them. Some of these languages have few speakers, while some have none. The learners of these languages are engaged in using documented resources (i.e. word lists, hymnals, bibles) to relearn their languages. Language proficiency in these cases of endangerment is being determined by how much language is learned in these communities through these efforts; proficient speakers are being determined by these communities. Organizations ACTFL The American Council on the Teaching of Foreign Languages (ACTFL) distinguishes between proficiency and performance. In part, ACTFL's definition of proficiency is derived from mandates issued by the U.S. government, declaring that a limited English proficient student is one who comes from a non-English background and "who has sufficient difficulty speaking, reading, writing, or understanding the English language and whose difficulties may deny such an individual the opportunity to learn successfully in classrooms where the language of instruction is English or to participate fully in our society". ACTFL views "performance" as being the combined effect of all three modes of communication: interpretive, interpersonal, and presentational. Proficiency frameworks Note